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/bsc_api.c b/openbsc/src/bsc_api.c
index 73b29b5..a9e5f71 100644
--- a/openbsc/src/bsc_api.c
+++ b/openbsc/src/bsc_api.c
@@ -520,7 +520,7 @@
 int gsm0808_clear(struct gsm_subscriber_connection *conn)
 {
 	if (conn->ho_lchan)
-		bsc_clear_handover(conn);
+		bsc_clear_handover(conn, 1);
 
 	if (conn->secondary_lchan)
 		lchan_release(conn->secondary_lchan, 0, 1);
@@ -633,8 +633,10 @@
 	/* now give up all channels */
 	if (conn->lchan == lchan)
 		conn->lchan = NULL;
-	if (conn->ho_lchan == lchan)
+	if (conn->ho_lchan == lchan) {
+		bsc_clear_handover(conn, 0);
 		conn->ho_lchan = NULL;
+	}
 	lchan->conn = NULL;
 
 	gsm0808_clear(conn);