Add getType to Topology interfaces.

Change-Id: If0726e99db224f790e66f0e8f8adca3864ff6f69
diff --git a/src/main/java/net/onrc/onos/core/topology/Port.java b/src/main/java/net/onrc/onos/core/topology/Port.java
index a8df75f..0ca5cce 100644
--- a/src/main/java/net/onrc/onos/core/topology/Port.java
+++ b/src/main/java/net/onrc/onos/core/topology/Port.java
@@ -14,7 +14,7 @@
  * Interface of Port object in the topology.
  */
 @JsonSerialize(using = PortSerializer.class)
-public interface Port extends StringAttributes {
+public interface Port extends ITopologyElement, StringAttributes {
 
     /**
      * Gets the data path ID (dpid) of the switch, which this port is on.