VOL-1520: Add missing call to start KPI/PM collection

Change-Id: Id3367e7b288b5cb0a3b35ad0bfe42bbbcefc31df
diff --git a/voltha/adapters/brcm_openomci_onu/brcm_openomci_onu_handler.py b/voltha/adapters/brcm_openomci_onu/brcm_openomci_onu_handler.py
index 0f759f3..d694938 100644
--- a/voltha/adapters/brcm_openomci_onu/brcm_openomci_onu_handler.py
+++ b/voltha/adapters/brcm_openomci_onu/brcm_openomci_onu_handler.py
@@ -229,6 +229,10 @@
             # Note, ONU ID and UNI intf set in add_uni_port method
             self._onu_omci_device.alarm_synchronizer.set_alarm_params(mgr=self.alarms,
                                                                       ani_ports=[self._pon])
+
+            # Start collecting stats from the device after a brief pause
+            reactor.callLater(10, self.pm_metrics.start_collector)
+
             self.enabled = True
         else:
             self.log.info('onu-already-activated')