[LTS] AMQPMessage.scanMessageData() creates unecessary buffer wrapper

The AMQPMessage.scanMessageData(ReadableBuffer) method creates an unecessary buffer wrapper on every decode. The method has the equivalent of:

decoder.setBuffer(data);
 try {
   //...use decoder..
 } finally {
   decoder.setByteBuffer(null);
 }

Effectively it tries to use the thread-local decoder, then ensure the related buffer is discarded after.

However the two setter uses are different, with the former taking the ReadableBuffer directly, and the latter method expected to be passed a ByteBuffer, which causes creation of a ReadableBuffer wrapper for it. By passing it null with that method, a needless wrapper object is created. One which is discarded on the next decode by that thread when it sets the next actual buffer. It should be using setBuffer(null).