dhtrunner: run shutdown in priority queue

Fix calling shutdown on a non-connected node.

src/dhtrunner.cpp

@@ -111,7 +111,7 @@ DhtRunner::run(const sockaddr_in* local4, const sockaddr_in6* local6, DhtRunner:
 void
 DhtRunner::shutdown(Dht::ShutdownCallback cb) {
     std::lock_guard<std::mutex> lck(storage_mtx);
-    pending_ops.emplace([=](SecureDht& dht) mutable {
+    pending_ops_prio.emplace([=](SecureDht& dht) mutable {
         dht.shutdown(cb);
     });
     cv.notify_all();