Handle tcp requests correctly in mdns
Handle tcp requests correctly in mdns

Tcp requests have an additional length field before the payload.  This
is not the case with udp requests.  In addition, tcp responses also
need to have the length field at the start of the response.

For now we handle only one packet tcp requests.

Change-Id: Iaf0e45c02a3a6bf627eb6a5dd7aa21f401d6ceef
Closes-Bug: 1344131

cneill/designate,grahamhayes/designate,cneill/designate,tonyli71/designate,openstack/designate,cneill/designate-testing,openstack/designate,cneill/designate-testing,kiall/designate-py3,tonyli71/designate,melodous/designate,melodous/designate,ionrock/designate,tonyli71/designate,melodous/designate,grahamhayes/designate,cneill/designate,kiall/designate-py3,cneill/designate,kiall/designate-py3,melodous/designate,ionrock/designate,ramsateesh/designate,grahamhayes/designate,muraliselva10/designate,ramsateesh/designate,ramsateesh/designate,openstack/designate,cneill/designate,ionrock/designate,cneill/designate-testing,muraliselva10/designate,muraliselva10/designate,kiall/designate-py3,kiall/designate-py3