Support passing a stop_cond function which can cause the
stream_collector to exit on a user-defined condition.
Signed-off-by: Leon Schuermann <leon@is.currently.online>
Also move test_stream/test_packet.
This allow keeping last_be (that will be replaced in the future) self-contained to LiteEth and will
also simplify the rework on Packetizer/Depacketizer in LiteX, application in LitePCIe and
future rework/application in LiteEth.