eScan: Handle large time frames

[mikaello]

Today a ringbuffer is used to store temporary data read from the eScan device, this has the downside that you need to now the max input size you can get, or we need smarter reading of large input frames (which could be several megabytes).

For the 250 and MTR4 this was OK, because those had predefined (and quite small) max sizes, the eScan time frames can be huge.