[SDFAB-355] Revisit MeterService and north abstractions

Change-Id: I685cb90d53f8aa61017ecda9fa7ff842e58e2940
diff --git a/core/api/src/main/java/org/onosproject/net/meter/Meter.java b/core/api/src/main/java/org/onosproject/net/meter/Meter.java
index 63b6db3..64379d3 100644
--- a/core/api/src/main/java/org/onosproject/net/meter/Meter.java
+++ b/core/api/src/main/java/org/onosproject/net/meter/Meter.java
@@ -37,7 +37,12 @@
         /**
          * Kilo bits per second.
          */
-        KB_PER_SEC
+        KB_PER_SEC,
+
+        /**
+         * Bytes per second.
+         */
+        BYTES_PER_SEC
     }
 
     /**
@@ -65,10 +70,13 @@
 
     /**
      * The id of the application which created this meter.
+     * Could be null if the meter is read from the controller southbound.
      *
      * @return an application id
      */
     ApplicationId appId();
+    // TODO: Deprecate this and create a new method returns an Optional ApplicationId
+    // TODO: Or introduce MeterEntry on south and keep this method
 
     /**
      * The unit used within this meter.