VOL-1172 Put ONU in UNREACHABLE state on openolt onu_indication down

Change-Id: I0e5d915e098e744de37cc851a61415aaf69a8580
diff --git a/voltha/adapters/openolt/openolt_device.py b/voltha/adapters/openolt/openolt_device.py
index bb4e629..b2d5204 100644
--- a/voltha/adapters/openolt/openolt_device.py
+++ b/voltha/adapters/openolt/openolt_device.py
@@ -493,6 +493,11 @@
 
         # Operating state
         if onu_indication.oper_state == 'down':
+
+            if onu_device.connect_status != ConnectStatus.UNREACHABLE:
+                onu_device.connect_status = ConnectStatus.UNREACHABLE
+                self.adapter_agent.update_device(onu_device)
+
             # Move to discovered state
             self.log.debug('onu-oper-state-is-down')