Fix disabling simulated ONU.

Change-Id: I5193051e22e1b6cea827da91a925bf3fdf339fc5
diff --git a/voltha/adapters/simulated_onu/simulated_onu.py b/voltha/adapters/simulated_onu/simulated_onu.py
index 9cc0e87..c2c462c 100644
--- a/voltha/adapters/simulated_onu/simulated_onu.py
+++ b/voltha/adapters/simulated_onu/simulated_onu.py
@@ -101,7 +101,8 @@
         raise NotImplementedError()
 
     def disable_device(self, device):
-        raise NotImplementedError()
+        device.oper_status = OperStatus.UNKNOWN
+        self.adapter_agent.update_device(device)
 
     def reenable_device(self, device):
         raise NotImplementedError()