pay-plugin: direct_pay only destination channels

The direct_pay payment modifier would query all peer channels, while
only the channels of the given peer suffices.

Changelog-None

plugins/libplugin-pay.c

@@ -3517,6 +3517,7 @@ static void direct_pay_cb(struct direct_pay_data *d, struct payment *p)
 				    direct_pay_listpeerchannels,
 				    direct_pay_listpeerchannels,
 				    p);
+	json_add_node_id(req->js, "id", p->route_destination);
 	send_outreq(p->plugin, req);
 }