[sccp] 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/include/sccp/sccp.h b/openbsc/include/sccp/sccp.h
index 5dfcc31..2aa0322 100644
--- a/openbsc/include/sccp/sccp.h
+++ b/openbsc/include/sccp/sccp.h
@@ -148,7 +148,7 @@
 u_int32_t sccp_src_ref_to_int(struct sccp_source_reference *ref);
 struct sccp_source_reference sccp_src_ref_from_int(u_int32_t);
 
-struct msgb *sccp_create_refuse(struct sccp_source_reference *src_ref, int cause);
+struct msgb *sccp_create_refuse(struct sccp_source_reference *src_ref, int cause, uint8_t *data, int length);
 
 /**
  * Below this are helper functions and structs for parsing SCCP messages