Support empty EtherNet/IP response frames, non-zero statuses
o When the cpppo.server.enip.client receives an empty EtherNet/IP frame
  or a non-zero status, log it appropriately.
o If a cpppo.server.enip --size <bytes> is provided, then limit the
  length of incoming encapsulated requests to the given size, and return
  a non-zero status if exceeded.
o If no server finds no response payload to return, demand a non-zero status
o Support empty/missing enip.input in enip_encode
o Version 2.7.0