[dht] Allow exceptions from DhtListener to propagate

If we propagate exceptions when sending dht messages
we can immediately time out requests when we fail to
send them.

src/MonoTorrent.Connections/MonoTorrent.Connections/UdpListener.cs

@@ -51,12 +51,12 @@ protected UdpListener (IPEndPoint endpoint)
 
         public async Task SendAsync (byte[] buffer, IPEndPoint endpoint)
         {
-            try {
-                if (endpoint.Address != IPAddress.Any)
-                    await Client.SendAsync (buffer, buffer.Length, endpoint).ConfigureAwait (false);
-            } catch (Exception ex) {
-                //logger.Exception (ex, "UdpListener could not send message");
-            }
+            if (Status == ListenerStatus.NotListening)
+                throw new InvalidOperationException ("You must invoke StartAsync before sending or receiving a message with this listener.");
+            if (Status == ListenerStatus.PortNotFree)
+                throw new InvalidOperationException ($"The listener could not bind to ${EndPoint}. Choose a new listening endpoint.");
+
+            await Client.SendAsync (buffer, buffer.Length, endpoint).ConfigureAwait (false);
         }
 
         protected override void Start (CancellationToken token)