Use immediateload for loading rules attribute

With recent changes in security group rules where it uses dynamic lazy
mode for fetching security group rules, joinedload cannot be used as it is
using joined eager loading

Change-Id: I73c585a6e8d32e7556968f775011b649195ada40

networking_arista/common/db_lib.py

@@ -19,7 +19,7 @@ from oslo_config import cfg
 from oslo_log import log as logging
 from sqlalchemy import and_, or_
 from sqlalchemy import func
-from sqlalchemy.orm import joinedload, Query, aliased
+from sqlalchemy.orm import immediateload, Query, aliased
 
 from neutron_lib.api.definitions import portbindings
 from neutron_lib import constants as n_const
@@ -485,10 +485,10 @@ def get_security_groups():
     session = db.get_reader_session()
     with session.begin():
         sg_model = sg_models.SecurityGroup
-        # We do a joined load to prevent the need for the sync worker
+        # We do an immediate load to prevent the need for the sync worker
         # to issue subqueries
         security_groups = (session.query(sg_model)
-                           .options(joinedload(sg_model.rules)))
+                           .options(immediateload(sg_model.rules)))
     return security_groups