Flow stats collection optimization - Flag introduced to stop periodic collection and collect only in 3 scenarios (Flows Add/Delete/Mod, Switch Add/Change, Mastership Change)

Change-Id: I1ad143a416f34135a622818c60dbc97310fe905e
diff --git a/protocols/openflow/api/src/main/java/org/onosproject/openflow/controller/driver/OpenFlowAgent.java b/protocols/openflow/api/src/main/java/org/onosproject/openflow/controller/driver/OpenFlowAgent.java
index 4451b19..d6bda5d 100644
--- a/protocols/openflow/api/src/main/java/org/onosproject/openflow/controller/driver/OpenFlowAgent.java
+++ b/protocols/openflow/api/src/main/java/org/onosproject/openflow/controller/driver/OpenFlowAgent.java
@@ -124,4 +124,11 @@
      * @param listener the OpenFlow classifier listener
      */
     void removeClassifierListener(OpenFlowClassifierListener listener);
+
+    /**
+     * Notify that role of the switch changed to Master.
+     *
+     * @param dpid the switch for which the role is changed
+     */
+    default void roleChangedToMaster(Dpid dpid) {}
 }