fix #2619: is there a problem in NettyBackedChannelBuffer.setBytes(...)? (#3448)

Author: beiwei30

dubbo-remoting/dubbo-remoting-netty/src/main/java/org/apache/dubbo/remoting/transport/netty/NettyBackedChannelBuffer.java

@@ -119,7 +119,7 @@ public void setBytes(int index, ChannelBuffer src, int srcIndex, int length) {
         // careful
         byte[] data = new byte[length];
         buffer.getBytes(srcIndex, data, 0, length);
-        setBytes(0, data, index, length);
+        setBytes(index, data, 0, length);
     }