Adding device type

Adding device type on port(eg Ethernet Port,TPort,WPort), Link(Ethernet,Optical..) and Switch(Ethernet,Optical)
Updated Serializers.
Fixed javadoc issue for Enums.

ONOS-1428

Change-Id: Id3e3094f1fbf90154fff9a61e3c0ca36be69c281
diff --git a/src/main/java/net/onrc/onos/core/topology/TopologyElement.java b/src/main/java/net/onrc/onos/core/topology/TopologyElement.java
index a9cfbf8..f70e7f5 100644
--- a/src/main/java/net/onrc/onos/core/topology/TopologyElement.java
+++ b/src/main/java/net/onrc/onos/core/topology/TopologyElement.java
@@ -38,6 +38,11 @@
 
     public static final String ELEMENT_ADMIN_STATUS = "AdminStatus";
 
+    /**
+     * Attribute name for device type.
+     */
+    public static final String ELEMENT_TYPE = "ElementType";
+
     private boolean isFrozen = false;
 
     private ConcurrentMap<String, String> stringAttributes;