Add DatagramChannel.isConnected()

.. because there is no way for a user with isActive to know if
   DatagramChannel is connected or not

transport/src/main/java/io/netty/channel/socket/DatagramChannel.java

@@ -35,6 +35,8 @@ public interface DatagramChannel extends Channel {
     @Override
     InetSocketAddress remoteAddress();
 
+    boolean isConnected();
+
     /**
      * Joins a multicast group.
      */

transport/src/main/java/io/netty/channel/socket/nio/NioDatagramChannel.java

@@ -112,6 +112,11 @@ public final class NioDatagramChannel
         return ch.isOpen() && ch.socket().isBound();
     }
 
+    @Override
+    public boolean isConnected() {
+        return javaChannel().isConnected();
+    }
+
     @Override
     protected DatagramChannel javaChannel() {
         return (DatagramChannel) super.javaChannel();

transport/src/main/java/io/netty/channel/socket/oio/OioDatagramChannel.java

@@ -109,6 +109,11 @@ public class OioDatagramChannel extends AbstractOioMessageChannel
         return isOpen() && socket.isBound();
     }
 
+    @Override
+    public boolean isConnected() {
+        return socket.isConnected();
+    }
+
     @Override
     protected SocketAddress localAddress0() {
         return socket.getLocalSocketAddress();