Comment 43 for bug 1953165

Reviewed: https://review.opendev.org/c/openstack/neutron/+/880964
Committed: https://opendev.org/openstack/neutron/commit/1d674825ebbe5fcab6c8fef7d03b5cf9b332b743
Submitter: "Zuul (22348)"
Branch: stable/xena

commit 1d674825ebbe5fcab6c8fef7d03b5cf9b332b743
Author: Bence Romsics <email address hidden>
Date: Mon Mar 6 13:04:01 2023 +0100

    Suppress IPv6 metadata DAD failure and delete address

    IPv4 DAD is non-existent in Linux or its failure is silent, so we
    never needed to catch and ignore it. On the other hand IPv6 DAD
    failure is explicit, hence comes this change.

    This of course leaves the metadata service dead on hosts where
    duplicate address detection failed. But if we catch the
    DADFailed exception and delete the address, at least other
    functions of the dhcp-agent should not be affected.

    With this the IPv6 isolated metadata service is not redundant, which
    is the best we can do without a redesign.

    Also document the promised service level of isolated metadata.

    Added additional tests for the metadata driver as well.

    Conflicts:
        neutron/tests/unit/agent/metadata/test_driver.py
            conflict with f430cd00725f8303f5313cb7784c9aed4b982e62

    Change-Id: I6b544c5528cb22e5e8846fc47dfb8b05f70f975c
    Partial-Bug: #1953165
    (cherry picked from commit 2aee961ab6942ab59aeacdc93d918c8c19023041)
    (cherry picked from commit 071255f098e0e73fd5220f83cbbc8ac1c421f3ab)
    (cherry picked from commit 1c615281f7632f3f1cf4bd37eefe90c50c6dfe25)
    (cherry picked from commit defb6018f3a395094cc85a03b93a2a0b43d2f6ff)