bsc: Add TC_{early,late}_conn_fail()

Those test cases simulate a BTS-originated RLL CONN FAIL IND at
"unusual" time:

a) before we actually establish any RLL
b) after / while we're tearing down the RLL

This is triggering an osmo-bsc segfault, see OS#3182.

Change-Id: I324c410d7565c189dbc91df577d92b87c036732c
Related: OS#3182
1 file changed