LAPDm: Fix re-establishment of datalink

If the datalink fails or if handover or assignment to a new channel fails,
it is re-establised by sending SABM again. The length of establish message
is 0 in this case. The length is used to differentiate between
re-establishment and contention resolution, which has to be handled
differently.

See TS 04.06 Chapter 5.4.2.1
1 file changed