Nova compute service plugs VIF on service init, it triggers
rules reinitialization for iptables filter. But it breaks
traffic in case isolate_vif is used by assigning dead VLAN
to the port. This patch prevents dead VLAN assingment
for ports that exists.
Co-Authored-By: aarefiev@mirantis.com
Closes-Bug: #2023300
Change-Id: Ib1b7467fce9facfbfcd698bf6e9f950c0cead650