TC_rsl_modify_encr BTS_Tests

Regression

Failing for the past 1 build since #648

Took 12 sec (from Titan)

Stack Trace

"BTS_Tests.ttcn:7761 : Timeout waiting for MODE MODIFY (N)ACK"
      BTS_Tests.ttcn:9456 BTS_Tests control part
      BTS_Tests.ttcn:7788 TC_rsl_modify_encr testcase