Fix ml2 & nec plugins for allowedaddresspairs tests

Enabling the allowedaddresspairs tests uncovered that update_port()
was not returning the expected updated port info (still contained
original info).

Change-Id: I88f252e1348d272edd114fbee69e2309d3740213
Closes-bug: #1255150
Merge "Fix ml2 & nec plugins for allowedaddresspairs tests"