[ONOS-3486] Add the annotation of port mac when monitor switch added.L3
flows need external port mac information.

Change-Id: I9afed351bd8d1641b8e9bef88718ec5c0ded8b5d
diff --git a/core/api/src/main/java/org/onosproject/net/AnnotationKeys.java b/core/api/src/main/java/org/onosproject/net/AnnotationKeys.java
index 4f81e92..38b599d 100644
--- a/core/api/src/main/java/org/onosproject/net/AnnotationKeys.java
+++ b/core/api/src/main/java/org/onosproject/net/AnnotationKeys.java
@@ -113,6 +113,11 @@
     public static final String PORT_NAME = "portName";
 
     /**
+     * Annotation key for the port mac.
+     */
+    public static final String PORT_MAC = "portMac";
+
+    /**
      * Annotation key for the router ID.
      */
     public static final String ROUTER_ID = "routerId";