Use proper logging placeholder for Netty logging

Author: ywelsch

modules/transport-netty4/src/main/java/org/elasticsearch/transport/netty4/Netty4Transport.java

@@ -323,7 +323,7 @@ protected void sendMessage(Channel channel, BytesReference reference, ActionList
                 final Throwable cause = f.cause();
                 Netty4Utils.maybeDie(cause);
                 logger.warn((Supplier<?>) () ->
-                    new ParameterizedMessage("write and flush on the network layer failed (channel: [])", channel), cause);
+                    new ParameterizedMessage("write and flush on the network layer failed (channel: {})", channel), cause);
                 assert cause instanceof Exception;
                 listener.onFailure((Exception) cause);
             }