Add getType to Topology interfaces.

Change-Id: If0726e99db224f790e66f0e8f8adca3864ff6f69
diff --git a/src/main/java/net/onrc/onos/core/topology/Link.java b/src/main/java/net/onrc/onos/core/topology/Link.java
index 8cd7b82..f54ff51 100644
--- a/src/main/java/net/onrc/onos/core/topology/Link.java
+++ b/src/main/java/net/onrc/onos/core/topology/Link.java
@@ -10,7 +10,7 @@
  * Interface of Link object in the topology.
  */
 @JsonSerialize(using = LinkSerializer.class)
-public interface Link extends StringAttributes {
+public interface Link extends ITopologyElement, StringAttributes {
     /**
      * Gets the source switch for the link.
      *