bsc: Clear the hand-over in case the new_lchan is failing

When the new_lchan for handover is failing we should stop the
handover operation. This is fixing a crash that we get a timeout
on the lchan and have no conn set to it. Introduce a flag to
the bsc_clear_handover to not free the lchan. In case the ho_lchan
is failing we do not want to call lchan_release as it would
reset the state.
diff --git a/openbsc/src/handover_logic.c b/openbsc/src/handover_logic.c
index 44a6933..c2e3f8c 100644
--- a/openbsc/src/handover_logic.c
+++ b/openbsc/src/handover_logic.c
@@ -149,7 +149,7 @@
 	return 0;
 }
 
-void bsc_clear_handover(struct gsm_subscriber_connection *conn)
+void bsc_clear_handover(struct gsm_subscriber_connection *conn, int free_lchan)
 {
 	struct bsc_handover *ho;
 
@@ -166,7 +166,9 @@
 
 	conn->ho_lchan->conn = NULL;
 	conn->ho_lchan = NULL;
-	lchan_release(ho->new_lchan, 0, 1);
+
+	if (free_lchan)
+		lchan_release(ho->new_lchan, 0, 1);
 
 	bsc_del_timer(&ho->T3103);
 	llist_del(&ho->list);