gtphub: ensure cleanup of peer addresses.

Upon calling gtphub_peer_del(), all addresses and ports should already have
expired (by force). Make sure the code heeds that with a so far missing
assertion.

Sponsored-by: On-Waves ehi

openbsc/src/gprs/gtphub.c

@@ -696,6 +696,7 @@ time_t gtphub_now(void)
 /* Remove a gtphub_peer from its list and free it. */
 static void gtphub_peer_del(struct gtphub_peer *peer)
 {
+	OSMO_ASSERT(llist_empty(&peer->addresses));
 	nr_map_clear(&peer->seq_map);
 	llist_del(&peer->entry);
 	talloc_free(peer);