rxrpc: Fix oops on incoming call to serviceless endpoint

If an call comes in to a local endpoint that isn't listening for any
incoming calls at the moment, an oops will happen.  We need to check that
the local endpoint's service pointer isn't NULL before we dereference it.
Signed-off-by: David Howells <dhowells@redhat.com>

net/rxrpc/call_accept.c

@@ -337,7 +337,7 @@ struct rxrpc_call *rxrpc_new_incoming_call(struct rxrpc_local *local,
 
 	/* Get the socket providing the service */
 	rx = rcu_dereference(local->service);
-	if (service_id == rx->srx.srx_service)
+	if (rx && service_id == rx->srx.srx_service)
 		goto found_service;
 
 	trace_rxrpc_abort("INV", sp->hdr.cid, sp->hdr.callNumber, sp->hdr.seq,