Netconf protocol handler maintains a buffer for replies that never shrinks

The buffer used by the protocol handler for NETCONF devices is reused (which is good), but as a consequence grows to the size of the largest reply ever received. As an example, if one reply grows the buffer to 1M, but all the other replies are under 16k then the buffer is maintained at 1M.

While this isn't critical, it would be nice if there was a memory management algorithm around this that would more aggressively manage the allocated size. for example, if over the past 100 replies the max size was X, maybe trim to that size.