fix update_port to get tenant_id from db rather than request

This patch changes the behavor of nvp's update_port() to how it previously
worked by retrieving the value from the db and not the request.

Fixes bug 1138330

Change-Id: I49682db392954b3cfaeb4ad4b8acf95113dcae7e
Merge "fix update_port to get tenant_id from db rather than request"