OvnDriver and DvrHaDriver to use "distributed_support" variable

``OvnDriver`` and ``DvrHaDriver`` classes were using an incorrect
variable name to define the DVR support, that should be
"distributed_support" instead of "dvr_support".

Closes-Bug: #2056199
Change-Id: Id2ee080dde8cd094995e94564f2877a89e9cc5aa

Author: ralonsoh

neutron/services/l3_router/service_providers/dvrha.py

@@ -19,4 +19,4 @@
 
 class DvrHaDriver(dvr.DvrDriver, ha.HaDriver):
     ha_support = base.MANDATORY
-    dvr_support = base.MANDATORY
+    distributed_support = base.MANDATORY

neutron/services/ovn_l3/service_providers/ovn.py

@@ -39,7 +39,7 @@
 @registry.has_registry_receivers
 class OvnDriver(base.L3ServiceProvider):
     ha_support = base.MANDATORY
-    dvr_support = base.MANDATORY
+    distributed_support = base.MANDATORY
 
     @registry.receives(resources.ROUTER, [events.PRECOMMIT_CREATE])
     def _process_router_create_precommit(self, resource, event, trigger,