set default for gw conn info in nvp_networkgw extension

Bug 1183285

This patch simply guarantees default segmentation type and
id in gateway connection info for the 'connect' and 'disconnect'
actions are correctly set respectively to 'flat' and 0.

Change-Id: I1b4e8274651e05f4681878ab70daef990ece901b
Merge "set default for gw conn info in nvp_networkgw extension"