Setup Json Serializers for Topology classes.
Add the appropriate annotation to specify the Json serializer for each
class; Device, Link, Port, Switch

Change-Id: I83fd36afc2ae58c7fef4e928ee0081f89c5d4c98
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 9734704..7782188 100644
--- a/src/main/java/net/onrc/onos/core/topology/Link.java
+++ b/src/main/java/net/onrc/onos/core/topology/Link.java
@@ -1,10 +1,14 @@
 package net.onrc.onos.core.topology;
 
+import net.onrc.onos.core.topology.serializers.LinkSerializer;
+import org.codehaus.jackson.map.annotate.JsonSerialize;
+
 // TODO Everything returned by these interfaces must be either Unmodifiable view,
 // immutable object, or a copy of the original "SB" In-memory Topology.
 /**
  * Interface of Link object in the topology.
  */
+@JsonSerialize(using = LinkSerializer.class)
 public interface Link {
     /**
      * Gets the source switch for the link.