Initial sketch of the virtual network constructs.

Change-Id: Ibcdafb9e56edb29fb37b80d7b0da321ad989c564
diff --git a/core/api/src/main/java/org/onosproject/net/Port.java b/core/api/src/main/java/org/onosproject/net/Port.java
index 87d7535..d70b1e1 100644
--- a/core/api/src/main/java/org/onosproject/net/Port.java
+++ b/core/api/src/main/java/org/onosproject/net/Port.java
@@ -53,7 +53,12 @@
          * Signifies optical fiber-based WDM port (called W-port).
          * Optical Multiplexing Section (See ITU G.709).
          */
-        OMS
+        OMS,
+
+        /**
+         * Signifies virtual port.
+         */
+        VIRTUAL
     }
 
     /**