VOL-1438 SEBA-344 Force mib reset on device re-enable

Workaround related to mib sync issues.  Given the omci library
now checks for MDS value on start (or restart) it skips the mib
reset needed to clear out of vlan config data.  Override the startup
method to unset the last mib sync value and forcing a resync and mib
upload

Change-Id: I07e47af56f219fb1f58cd0d310a377c7118c71fa
diff --git a/voltha/adapters/brcm_openomci_onu/omci/brcm_mib_sync.py b/voltha/adapters/brcm_openomci_onu/omci/brcm_mib_sync.py
index 53ca22d..1898c52 100644
--- a/voltha/adapters/brcm_openomci_onu/omci/brcm_mib_sync.py
+++ b/voltha/adapters/brcm_openomci_onu/omci/brcm_mib_sync.py
@@ -41,6 +41,15 @@
         super(BrcmMibSynchronizer, self).__init__(agent, device_id, mib_sync_tasks, db,
                                                   advertise_events=advertise_events)
 
+    def on_enter_starting(self):
+        """
+        Given resync and mib update is questionable (see below) flag the ONU as a new device which forces a mib
+        reset and a mib upload
+        """
+        self.log.warn('db-sync-not-supported-forcing-reset')
+        self._last_mib_db_sync_value = None
+        super(BrcmMibSynchronizer, self).on_enter_starting()
+
     def on_enter_auditing(self):
         """
         Perform a MIB Audit.  Currently this is broken on BRCM based onu and its never in sync and continuously