[OVN] Add availability zone to the ML2_SUPPORTED_API_EXTENSIONS list
[OVN] Add availability zone to the ML2_SUPPORTED_API_EXTENSIONS list

Currently in the ML2_SUPPORTED_API_EXTENSIONS which is list of
extensions supported by OVN mech driver there was
network_availability_zone extension. But that extension requires
availability_zone extension which was added only in
ML2_SUPPORTED_API_EXTENSIONS_OVN_L3 which is list of extensions
supported by the OVN L3 plugin.
To fix that, this patch adds availability_zone extension to the
ML2_SUPPORTED_API_EXTENSIONS list also.

Related-Bug: #1929676
Change-Id: If815cff18f83962233f3d6a535b18070690ce948

mahak/neutron,mahak/neutron,openstack/neutron,openstack/neutron,openstack/neutron,mahak/neutron