Enable port-forwarding extension for OVN

The floating IP port forwarding extension in Neutron started
supporting OVN in the Victoria timeframe [0], but the charm
code was never updated, it always disables it.

Since we have people that want to use it in OVN deployments,
we should allow it to be enabled back to Yoga.

[0] https://review.opendev.org/c/openstack/neutron/+/724445

Closes-bug: #2083283
Change-Id: I365167afc197f1422764ad4c86bc5c597e17f00e

src/lib/charm/openstack/neutron_api_plugin_ovn.py

@@ -84,8 +84,6 @@ class BaseNeutronAPIPluginCharm(charms_openstack.charm.OpenStackCharm):
         'firewall_v2',
         # Security groups logging not supported at this time
         'log',
-        # Port forwarding is not supported at this time
-        'port_forwarding',
         # OVN has its own service driver for that replaces Neutron ``router``
         'router',
         # VPNaaS is not supported

unit_tests/test_lib_charm_openstack_ovn.py

@@ -124,6 +124,7 @@ class TestNeutronAPIPluginOvnCharm(Helper):
             'metering',
             'segments',
             'lbaasv2',
+            'port_forwarding',
             'ovn-router',
         ]
         self.assertEqual(c.service_plugins(svc_plugins), expect)