On a recent change [1], some additional checks was added to avoid
ports overlapping cidrs on a router. On this change was also added
a check to do not attach more than one port IPv6 from same network,
but this check need to allow multiple ports when a deployment is
done using ml2/ovs+xvlan+dvr and the router has an external gateway
configured, because two ports are added:
- one with device_owner as network:router_interface_distributed
- another one with device_owner as network:router_centralized_snat
Also an small improvement is done for just run this check over the
existing ports on the router for the same network_id.
[1] https://review.opendev.org/c/openstack/neutron/+/859143
Closes-Bug: #2002800
Change-Id: I765a7b41e7e84f42a3180dfd15e3a41a8e085284
(cherry picked from commit e2097157bb)