lchan_fsm: notify conn of released lchan upon RF Release

Related: osmo-ttcn3-hacks If772dbbc5f9790d3f911465e1303dd0a99811154
Change-Id: I7621616c24588c2db15ad1ae7ca68cfa0fb76f66
diff --git a/src/osmo-bsc/lchan_fsm.c b/src/osmo-bsc/lchan_fsm.c
index 9f2d6c3..39edaff 100644
--- a/src/osmo-bsc/lchan_fsm.c
+++ b/src/osmo-bsc/lchan_fsm.c
@@ -993,6 +993,13 @@
 {
 	int rc;
 	struct gsm_lchan *lchan = lchan_fi_lchan(fi);
+
+	/* For planned releases, a conn has already forgotten about the lchan. And later on, in
+	 * lchan_reset(), we make sure it does. But in case of releases from error handling, the
+	 * conn might as well notice now already that its lchan is becoming unusable. */
+	if (lchan->conn)
+		gscon_forget_lchan(lchan->conn, lchan);
+
 	rc = rsl_tx_rf_chan_release(lchan);
 	if (rc)
 		LOG_LCHAN(lchan, LOGL_ERROR, "Failed to Tx RSL RF Channel Release: rc=%d %s\n",