[VOL-3153]Update pm config fails for openonu device

Change-Id: I47201ac109e01e5ea331d927d4fb348f9b82494b
diff --git a/pyvoltha/adapters/extensions/events/kpi/onu/onu_omci_pm.py b/pyvoltha/adapters/extensions/events/kpi/onu/onu_omci_pm.py
index b95dae3..cfa3c7a 100644
--- a/pyvoltha/adapters/extensions/events/kpi/onu/onu_omci_pm.py
+++ b/pyvoltha/adapters/extensions/events/kpi/onu/onu_omci_pm.py
@@ -119,8 +119,8 @@
         if self.default_freq != pm_config.default_freq:
             # Update the callback to the new frequency.
             self.default_freq = pm_config.default_freq
-            self.lc.stop()
-            self.lc.start(interval=self.default_freq / 10)
+            self.stop_collector()
+            self.start_collector()
 
         if pm_config.grouped:
             for group in pm_config.groups: