CC: intentionally release T308 on BSSMAP Clear Request from BSC

So far we hit a running T308 during CC release when caused by a BSSMAP Clear
Request, and we loudly log that as error.

However, now I understand that T308 is a direct cause of the dispatch of a REL
IND towards MNCC, which is used to indicate teardown to MNCC. So during
_gsm48_cc_trans_free(), we first clear all timers, then invoke
mncc_release_ind() which starts another timer (useful for graceful CC Release,
but in this code path the intention is immediate release). Simply immediately
cancel the timer again and release the conn.

A separate question is whether a BSSMAP Clear Request should be less aggressive
in releasing the connections; i.e. instead of calling trans_free() all around,
to rather ask each transaction to "please stop soon", somehow.

Related: OS#3062
Change-Id: I231fdb574a086a206321148474cbdc7ca9cf39f0
3 files changed