To enable this feature:
1. set oslo_messaging_notifications driver in the neutron.conf
2. set support_nsx_port_tagging to true in the nsx.ini
Use the neutron tagging plugin to set a tag on a neutron port.
The tag should have the format of '<tag_scope>:<tag value>'
Change-Id: I89e24bc7f3eeb363dd05748d77bd683a236934a0