Pack the Nodes message more tightly

[Nashatyrev]

Description

Currently ENRs for Nodes message are packed considering the max ENR size, i.e. max 4 ENRs per packet to fit the max packet size in the worst case.
If ENRs are smaller then more records could be packed into a single message.

Also need to consider that the message can be sent withing both OrdinaryMessage and Handshake packets. However for Nodes message (as a response message) this situation is highly unlikely to occur with a honest remote node, so probably just controlling and dropping outgoing too large message would be enough. (see comment #72 (comment))

[atoulme]

Please note also that if all buckets are empty, the discovery lib sends several Nodes message. This is because of this line:
if (total % MAX_NODES_PER_MESSAGE == 0) {

On my end I see this:

01:34:23.394 [DefaultDispatcher-worker-5 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received message from /192.168.88.236:9000
01:34:23.409 [DefaultDispatcher-worker-5 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received message of type NODES
01:34:23.411 [DefaultDispatcher-worker-5 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received message from /192.168.88.236:9000
01:34:23.412 [DefaultDispatcher-worker-5 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received message of type NODES
01:34:23.412 [DefaultDispatcher-worker-5 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received NODES message but no matching FINDNODES present. Dropping
01:34:23.413 [DefaultDispatcher-worker-5 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received message from /192.168.88.236:9000
01:34:23.414 [DefaultDispatcher-worker-5 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received message of type NODES
01:34:23.414 [DefaultDispatcher-worker-5 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received NODES message but no matching FINDNODES present. Dropping
01:34:23.416 [DefaultDispatcher-worker-6 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received message from /192.168.88.236:9000
01:34:23.417 [DefaultDispatcher-worker-6 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received message of type NODES
01:34:23.417 [DefaultDispatcher-worker-6 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received NODES message but no matching FINDNODES present. Dropping
01:34:23.429 [DefaultDispatcher-worker-6 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received message from /192.168.88.236:9000
01:34:23.430 [DefaultDispatcher-worker-6 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received message of type NODES
01:34:23.430 [DefaultDispatcher-worker-6 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received NODES message but no matching FINDNODES present. Dropping
01:34:23.453 [DefaultDispatcher-worker-6 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received message from /192.168.88.236:9000
01:34:23.454 [DefaultDispatcher-worker-6 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received message of type NODES
01:34:23.455 [DefaultDispatcher-worker-6 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received NODES message but no matching FINDNODES present. Dropping
01:34:23.466 [DefaultDispatcher-worker-4 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received message from /192.168.88.236:9000
01:34:23.468 [DefaultDispatcher-worker-4 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received message of type NODES
01:34:23.530 [DefaultDispatcher-worker-4 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received message from /192.168.88.236:9000
01:34:23.531 [DefaultDispatcher-worker-4 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received message of type NODES
01:34:23.531 [DefaultDispatcher-worker-4 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received NODES message but no matching FINDNODES present. Dropping
01:34:23.663 [DefaultDispatcher-worker-4 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received message from /192.168.88.236:9000
01:34:23.664 [DefaultDispatcher-worker-4 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received message of type NODES
01:34:23.664 [DefaultDispatcher-worker-4 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received NODES message but no matching FINDNODES present. Dropping
01:34:23.664 [DefaultDispatcher-worker-4 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received message from /192.168.88.236:9000
01:34:23.665 [DefaultDispatcher-worker-4 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received message of type NODES
01:34:23.665 [DefaultDispatcher-worker-4 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received NODES message but no matching FINDNODES present. Dropping
01:34:23.676 [DefaultDispatcher-worker-7 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received message from /192.168.88.236:9000
01:34:23.677 [DefaultDispatcher-worker-7 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received message of type NODES
01:34:23.677 [DefaultDispatcher-worker-7 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received NODES message but no matching FINDNODES present. Dropping
01:34:23.693 [DefaultDispatcher-worker-7 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received message from /192.168.88.236:9000
01:34:23.693 [DefaultDispatcher-worker-7 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received message of type NODES
01:34:23.693 [DefaultDispatcher-worker-7 @coroutine#2] TRACE org.apache.tuweni.devp2p.v5.Session - Received NODES message but no matching FINDNODES present. Dropping

[Nashatyrev]

@atoulme thanks for the case!
This code was refactored so this issue shouldn't be reproducible on the upcoming 5.1 version:
https://github.com/PegaSysEng/discovery/blob/e59a075f01423b33af7abdc0cb54c8bc3c140a60/src/main/java/org/ethereum/beacon/discovery/message/handler/FindNodeHandler.java#L43

The following test should cover this case:
https://github.com/PegaSysEng/discovery/blob/1c83b49d814359963777df00d49a660242ef6cb9/src/test/java/org/ethereum/beacon/discovery/message/handler/FindNodeHandlerTest.java#L130