lchan: Introduce T3109 handling for the release procedure

T3109 is started when the SACCH is deactivated. It is stopped when
the phones sends the DISC/UA/UM on LAPDm for the main signalling
link. In case of timeout the abnormal release procedure will be
initiated. Make sure to not issue the SACCH Deactivate twice to
avoid confusing the equipment.

This is still not fully spec compliant. In case of a timeout the
abnormal release handling will be started which involves starting
T3111+2. The error handling should be split out of the rf channel
release method, e.g. lchan_release should be called and check if
the channel release was already initiated.
diff --git a/openbsc/doc/examples/osmo-nitb/nanobts/openbsc-multitrx.cfg b/openbsc/doc/examples/osmo-nitb/nanobts/openbsc-multitrx.cfg
index 7a187f8..bea0b7d 100644
--- a/openbsc/doc/examples/osmo-nitb/nanobts/openbsc-multitrx.cfg
+++ b/openbsc/doc/examples/osmo-nitb/nanobts/openbsc-multitrx.cfg
@@ -30,7 +30,7 @@
  timer t3103 0
  timer t3105 0
  timer t3107 0
- timer t3109 0
+ timer t3109 4
  timer t3111 0
  timer t3113 60
  timer t3115 0