BTS: pcu_rr_suspend clean up and release the channel

The testcase failed becaues of an unexpected RSL Error Indication from
the LAPDm system which was in the RSL emulation queue when tearing down
the test environment.
By calling f_rsl_chan_deact() the queue gets flushed until the RSL
deactivate channel is received. It's also more clean to release the
channel.

Fixes: OS#4051
Change-Id: I55827626803ca81b68f905fd0df3126367951f39
1 file changed