Add unit test for unpack and stick pack of dubbo and telent (#3703)

Author: maoyiz

dubbo-remoting/dubbo-remoting-netty4/src/main/java/org/apache/dubbo/remoting/transport/netty4/NettyCodecAdapter.java

@@ -33,7 +33,7 @@
 /**
  * NettyCodecAdapter.
  */
-final class NettyCodecAdapter {
+final public class NettyCodecAdapter {
 
     private final ChannelHandler encoder = new InternalEncoder();