[OVN] HAChassisGroupRouterEvent is for router HCG only

The event ``HAChassisGroupRouterEvent`` handles the ``HA_Chassis_Group``
registers created for routers, when the external network is tunnelled.
This event should only attend ``HA_Chassis_Group`` that have the key
"neutron:router_id" in the external_ids field, that identifies that is
created for routers only.

Closes-Bug: #2126588
Signed-off-by: Rodolfo Alonso Hernandez <[email protected]>
Change-Id: I4631094d7e2bfda9ddff5feb8c96960ea0cd436d
(cherry picked from commit d7e8042)

Author: ralonsoh

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

@@ -693,8 +693,10 @@ def __init__(self, driver):
         self.event_name = 'HAChassisGroupRouterEvent'
 
     def match_fn(self, event, row, old):
-        if (ovn_const.OVN_ROUTER_ID_EXT_ID_KEY in row.external_ids or
-                hasattr(old, 'ha_chassis')):
+        if ovn_const.OVN_ROUTER_ID_EXT_ID_KEY not in row.external_ids:
+            # This is not a router "HA_Chassis_Group".
+            return False
+        if hasattr(old, 'ha_chassis'):
             # "HA_Chassis_Group" has been assigned to a router or there are
             # changes in the "ha_chassis" list.
             return True