It looks like the neutron client bug. The function "take_action" in the class SetGatewayRouter doesn't pass the extra arguments to the neutron api, it caused the "router_gateway_set" command have no invalid attributes validation.
It looks like the neutron client bug. The function "take_action" in the class SetGatewayRouter doesn't pass the extra arguments to the neutron api, it caused the "router_ gateway_ set" command have no invalid attributes validation.