Register Chassis_Private table in BaseOvnSbIdl

As of Ib3c6f0dc01efd31430691e720ba23ccb4ede65fa, the
MaintenanceWorker checks for Chassis_Private table support and
uses it to remove duplicate Chassis/Chassis_Private entries. The
Chassis_Private table was not monitored in the BaseOvnSbIdl class
which the MaintenanceWorker uses.

Closes-Bug: #2049265
Change-Id: I711996b7644e80bc195833e4429e4d745728f9cf
(cherry picked from commit 60eb15e)

Author: otherwiseguy

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

@@ -666,6 +666,8 @@ def notify(self, event, row, updates=None):
 class BaseOvnSbIdl(Ml2OvnIdlBase):
     @classmethod
     def from_server(cls, connection_string, helper):
+        if 'Chassis_Private' in helper.schema_json['tables']:
+            helper.register_table('Chassis_Private')
         helper.register_table('Chassis')
         helper.register_table('Encap')
         helper.register_table('Port_Binding')