Fix DiagPktHandler::Reply to send complete packet
Fix DiagPktHandler::Reply to send complete packet

Issue:
------
Incorrect length alteration in DiagPktHandler::Reply
results in test_ping UT failure. it receives a packet
with data + udp/tcp header, however it tries to alter
length by substracting twice the agent header length
resulting it to send partial packet back.

increasing length of agent header further results in
length validation failure in test_ping

Fix:
----
removing length alteration to send the complete packet

Pratial-Bug: 1554423
Change-Id: Ic059e4e3e94955a965793bc8ffa418249a588843

nischalsheth/contrail-controller,nischalsheth/contrail-controller,codilime/contrail-controller,eonpatapon/contrail-controller,nischalsheth/contrail-controller,rombie/contrail-controller,eonpatapon/contrail-controller,nischalsheth/contrail-controller,rombie/contrail-controller,codilime/contrail-controller,nischalsheth/contrail-controller,rombie/contrail-controller,codilime/contrail-controller,rombie/contrail-controller,eonpatapon/contrail-controller,nischalsheth/contrail-controller,eonpatapon/contrail-controller,nischalsheth/contrail-controller,codilime/contrail-controller,nischalsheth/contrail-controller,codilime/contrail-controller,eonpatapon/contrail-controller,rombie/contrail-controller,codilime/contrail-controller,rombie/contrail-controller,eonpatapon/contrail-controller,eonpatapon/contrail-controller,rombie/contrail-controller