move osmo_gsup_addr_send() declaration from luop.h to gsup_router.h

Change-Id: I33165b7b58bd8c863083ed50ce21e3c032c579f5
diff --git a/src/gsup_router.h b/src/gsup_router.h
index 7a5bd25..f177347 100644
--- a/src/gsup_router.h
+++ b/src/gsup_router.h
@@ -6,3 +6,7 @@
 
 /* delete all routes for the given connection */
 int gsup_route_del_conn(struct osmo_gsup_conn *conn);
+
+int osmo_gsup_addr_send(struct osmo_gsup_server *gs,
+			const uint8_t *addr, size_t addrlen,
+			struct msgb *msg);