In order to implement VOLTHA VOL-949 task (https://jira.opencord.org/browse/VOL-949) , OltPipeline (pmc-olt driver) must support meter, transition and also QinQ vlan push instructions.

Change-Id: Ie027469fa190a78b0c8366da55431ebc62e699ef
diff --git a/core/api/src/main/java/org/onosproject/net/meter/MeterEvent.java b/core/api/src/main/java/org/onosproject/net/meter/MeterEvent.java
index fe4fb7b..a380f2d 100644
--- a/core/api/src/main/java/org/onosproject/net/meter/MeterEvent.java
+++ b/core/api/src/main/java/org/onosproject/net/meter/MeterEvent.java
@@ -42,7 +42,12 @@
         /**
          * A meter was finally removed from device.
          */
-        METER_REMOVED
+        METER_REMOVED,
+
+        /**
+         * Meter is not used by any flow. It can be deleted.
+         */
+        METER_REFERENCE_COUNT_ZERO
     }