[stable][ovn] frequent OVN DB leader changes increase rate of Neutron API errors

[Frode Nordahl]

Open vSwitch v2.16 introduces a change of behavior for clustered databases,
before the leader creates a snapshot of the database it will transfer
leadership to a different server.

For versions of Neutron where the Southbound DB IDL requires a connection to
the leader this will cause frequent reconnection. In a loaded system this will
subsequently lead to increased rate of API errors for the neutron-server
and delays for the neutron-ovn-metadata agent which manifest itself as
instances not getting metadata.

In the main branch Neutron has recently changed to not require a connection to
the leader for the Southbound DB [0].

End users can choose to use more recent versions of OVS and OVN than what was
available at the time of release of past OpenStack releases, so we would like
to have this change backported to Ussuri.

This bug is to track the backport of the change.

0: https://review.opendev.org/c/openstack/neutron/+/803268

[Frode Nordahl (fnordahl)]

Fix proposed to branch: stable/xena
Review: https://review.opendev.org/c/openstack/neutron/+/829486

Fix proposed to branch: stable/wallaby
Review: https://review.opendev.org/c/openstack/neutron/+/829487

Fix proposed to branch: stable/victoria
Review: https://review.opendev.org/c/openstack/neutron/+/829488

Fix proposed to branch: stable/ussuri
Review: https://review.opendev.org/c/openstack/neutron/+/829489

[Edward Hope-Morley (hopem)]

these patches are merged and released in ubuntu

[Edward Hope-Morley (hopem)]

See https://bugs.launchpad.net/ubuntu/+source/neutron/+bug/1975594