TC_sabm_retransmit BTS_Tests_LAPDm

Failing for the past 3 builds since #2720

Took 40 sec (from Titan)

Stack Trace

FBSB Failed with non-zero return code 255
      BTS_Tests_LAPDm.ttcn:1349 BTS_Tests_LAPDm control part
      BTS_Tests_LAPDm.ttcn:229 TC_sabm_retransmit testcase