bsc: check channel release message presence

Instead of vaguely allowing any release messages to be present or not, exactly
pinpoint for each test case the exact release messages expected during lchan
release.

Related: an osmo-bsc change broke sending of RR Release messages, which was
utterly ignored and hence not caught by ttcn tests. That must not happen again.

I am not actually sure that these expectations are 100% correct; if errors
become apparent, we shall change the expectations in ttcn3 and then fix
osmo-bsc according to that.

Adjust f_expect_chan_rel() and callers,
and the Assignment procedures (as_assignment and f_establish_fully).

The current state of the bsc tests should all pass with osmo-bsc
Id3301df059582da2377ef82feae554e94fa42035

Related: OS#3413
Change-Id: Ibc64058f1e214bea585f4e8dcb66f3df8ead3845
2 files changed