abis_rsl: Allow to specify the release mode for a given channel.

This can be used by handover, early assignment to indicate the
close of the old channel...
diff --git a/openbsc/src/chan_alloc.c b/openbsc/src/chan_alloc.c
index 107abdc..5a3e727 100644
--- a/openbsc/src/chan_alloc.c
+++ b/openbsc/src/chan_alloc.c
@@ -363,7 +363,7 @@
 
 	DEBUGP(DRLL, "%s Recycling Channel\n", gsm_lchan_name(lchan));
 	rsl_lchan_set_state(lchan, LCHAN_S_REL_REQ);
-	rsl_release_request(lchan, 0);
+	rsl_release_request(lchan, 0, 0);
 	return 1;
 }