rsl: Avoid double channel release procedure in error conditions

When we receive an ERROR INDICATION and CONNECTION FAILURE we
might call rsl_rf_chan_release multiple times. The channel release
handling is still a bit messy and there too many paths that lead
to the call.

1.) In case we receive an ERROR INDICATION for SAPI=3. A RLL
error signal will be emitted that leads to the release of the
channel through the SMS code in case of the NITB.  The call to
rsl_rf_chan_release might be a double release.

2.) In case a CONNECTION FAILURE is received when the release
process has already been started we would unconditionally
call rsl_rf_chan_release as well.

Because the lchan state is changed by the callers of the
rsl_rf_chan_release we can not move the state checking into this
code but need to do it in the caller. The issue was seen in a trace
from Rhizomatica and I created the DoubleRelease.st to re-produce
the issue and verified that we have no duplicate RF Channel Releses.

The other option would be to introduce a new state to track
the release process and see if we have already released SAPIs
deactivated the SACCH or such. We can not simply look at these
as for a channel that fails to activate they will be null already.

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