[stable only] Fix KeyError in set_gateway_mtu

Got missed in initial fixes[1], this patch fixes
it.

[1] https://review.opendev.org/q/I447990509cdea9830228d3bc92a97062cc57a472
Closes-Bug: #2065701
Related-Bug: #2060163

Change-Id: Icdab45ab0873c003977e3f02277d267116002973

Author: karelyatin

neutron/plugins/ml2/drivers/ovn/mech_driver/ovsdb/ovn_client.py

@@ -2059,7 +2059,7 @@ def set_gateway_mtu(self, context, prov_net, txn=None):
             lrp_name = utils.ovn_lrouter_port_name(port['id'])
             options = self._gen_router_port_options(port, prov_net)
             commands.append(self._nb_idl.update_lrouter_port(
-                lrp_name, if_exists=True, **options))
+                lrp_name, if_exists=True, options=options))
         self._transaction(commands, txn=txn)
 
     def _check_network_changes_in_ha_chassis_groups(self,

neutron/tests/unit/plugins/ml2/drivers/ovn/mech_driver/test_mech_driver.py

@@ -2574,7 +2574,7 @@ def _test_update_network_fragmentation(self, new_mtu, expected_opts, grps,
 
                 lrp_name = ovn_utils.ovn_lrouter_port_name(port['port']['id'])
                 self.nb_ovn.update_lrouter_port.assert_called_once_with(
-                    lrp_name, if_exists=True, **expected_opts)
+                    lrp_name, if_exists=True, options=expected_opts)
 
     def test_update_network_need_to_frag_enabled(self):
         ovn_conf.cfg.CONF.set_override('ovn_emit_need_to_frag', True,