CORD-1438 fix bug in Network model policy

Change-Id: I323922afdbb07ff3d56a45394819a5e028408ff6
diff --git a/xos/synchronizer/model_policies/model_policy_Network.py b/xos/synchronizer/model_policies/model_policy_Network.py
index 4000596..606fec8 100644
--- a/xos/synchronizer/model_policies/model_policy_Network.py
+++ b/xos/synchronizer/model_policies/model_policy_Network.py
@@ -23,7 +23,7 @@
         existing_controllers = []
         for cn in ControllerNetwork.objects.all():
             if cn.network.id == network.id:
-                existing_controllers.append(controller)
+                existing_controllers.append(cn.controller)
 
         existing_controller_ids = [c.id for c in existing_controllers]