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/src/libbsc/gsm_04_08_utils.c b/openbsc/src/libbsc/gsm_04_08_utils.c
index 968e62e..de596de 100644
--- a/openbsc/src/libbsc/gsm_04_08_utils.c
+++ b/openbsc/src/libbsc/gsm_04_08_utils.c
@@ -231,11 +231,7 @@
 		lchan->nr, lchan->type);
 
 	/* Send actual release request to MS */
-	gsm48_sendmsg(msg);
-	/* FIXME: Start Timer T3109 */
-
-	/* Deactivate the SACCH on the BTS side */
-	return rsl_deact_sacch(lchan);
+	return gsm48_sendmsg(msg);
 }
 
 int send_siemens_mrpci(struct gsm_lchan *lchan,