[sccp/nat] Make it optional to send data on a SCCP Connection Refuse

This can be used to send a Location Updating Reject down to the
BSC when it is clear that a subscriber is not allowed.
diff --git a/openbsc/src/nat/bsc_nat.c b/openbsc/src/nat/bsc_nat.c
index f21fe02..797cc2c 100644
--- a/openbsc/src/nat/bsc_nat.c
+++ b/openbsc/src/nat/bsc_nat.c
@@ -677,7 +677,7 @@
 
 exit3:
 	/* send a SCCP Connection Refused */
-	refuse = sccp_create_refuse(parsed->src_local_ref, SCCP_REFUSAL_SCCP_FAILURE);
+	refuse = sccp_create_refuse(parsed->src_local_ref, SCCP_REFUSAL_SCCP_FAILURE, NULL, 0);
 	if (refuse) {
 		bsc_send_data(bsc, refuse->l2h, msgb_l2len(refuse), IPAC_PROTO_SCCP);
 		msgb_free(refuse);