bsc: expect proper chan_nr for various RSL_MT_RF_CHAN_REL

So far we were often just expecting the message type. Instead expect a
release on the proper channel number.

While hunting a test error, this confused me for a while, because a
missing handler resulted in the release message handled in the wrong
place, even though the chan_nr mismatched.

Related: SYS#5130
Change-Id: I002c9273a387104bea062dec8879b4e19a72008d
1 file changed