A recent change suppressed the IPv6 DAD failure and
removed the address when multiple DHCP agents were
configured on the same network,
https://review.opendev.org/c/openstack/neutron/+/880957
But it also changed the behavior to not enable IPv4
metadata in this case. Restore the old behavior by
not returning early in the DAD failure case. The callback
that builds the config file was moved until after
the address was bound to make the two steps more obvious.
Related-bug: #1953165
Change-Id: I8436c6c9da9a2533ca27ff7312f5b2c7ea41e94f
846003c437