[ONOS-6472] Flow, table, group and meter stats collector stopped after starting

Change-Id: I74c638662b6980d1895291e55e8aa5c203f1e40b
diff --git a/providers/openflow/group/src/main/java/org/onosproject/provider/of/group/impl/OpenFlowGroupProvider.java b/providers/openflow/group/src/main/java/org/onosproject/provider/of/group/impl/OpenFlowGroupProvider.java
index 46abc77..cabd8dc 100644
--- a/providers/openflow/group/src/main/java/org/onosproject/provider/of/group/impl/OpenFlowGroupProvider.java
+++ b/providers/openflow/group/src/main/java/org/onosproject/provider/of/group/impl/OpenFlowGroupProvider.java
@@ -375,8 +375,8 @@
             }
             if (isGroupSupported(sw)) {
                 GroupStatsCollector gsc = new GroupStatsCollector(sw, POLL_INTERVAL);
-                gsc.start();
                 stopCollectorIfNeeded(collectors.put(dpid, gsc));
+                gsc.start();
             }
 
             //figure out race condition