mac80211: don't update the PM state of a peer upon a multicast frame

I changed the way mac80211 updates the PM state of the peer.
I forgot that we could also have multicast frames from the
peer and that those frame should of course not change the
PM state of the peer: A peer goes to power save when it
needs to scan, but it won't send the broadcast Probe Request
with the PM bit set.

This made us mark the peer as awake when it wasn't and then
Intel's firmware would fail to transmit because the peer is
asleep according to its database. The driver warned about
this and it looked like this:

 WARNING: CPU: 0 PID: 184 at /usr/src/linux-4.16.14/drivers/net/wireless/intel/iwlwifi/mvm/tx.c:1369 iwl_mvm_rx_tx_cmd+0x53b/0x860
 CPU: 0 PID: 184 Comm: irq/124-iwlwifi Not tainted 4.16.14 #1
 RIP: 0010:iwl_mvm_rx_tx_cmd+0x53b/0x860
 Call Trace:
  iwl_pcie_rx_handle+0x220/0x880
  iwl_pcie_irq_handler+0x6c9/0xa20
  ? irq_forced_thread_fn+0x60/0x60
  ? irq_thread_dtor+0x90/0x90

The relevant code that spits the WARNING is:

        case TX_STATUS_FAIL_DEST_PS:
                /* the FW should have stopped the queue and not
                 * return this status
                 */
                WARN_ON(1);
                info->flags |= IEEE80211_TX_STAT_TX_FILTERED;

This fixes https://bugzilla.kernel.org/show_bug.cgi?id=199967.

Fixes: 9fef654 ("mac80211: always update the PM state of a peer on MGMT / DATA frames")
Cc: <[email protected]>   #4.16+
Signed-off-by: Emmanuel Grumbach <[email protected]>
Signed-off-by: Johannes Berg <[email protected]>

net/mac80211/rx.c

@@ -1612,6 +1612,7 @@ ieee80211_rx_h_sta_process(struct ieee80211_rx_data *rx)
 	 */
 	if (!ieee80211_hw_check(&sta->local->hw, AP_LINK_PS) &&
 	    !ieee80211_has_morefrags(hdr->frame_control) &&
+	    !is_multicast_ether_addr(hdr->addr1) &&
 	    (ieee80211_is_mgmt(hdr->frame_control) ||
 	     ieee80211_is_data(hdr->frame_control)) &&
 	    !(status->rx_flags & IEEE80211_RX_DEFERRED_RELEASE) &&