Change "type" constant name

Change-Id: Ia8a070d5d1937b68c0e77be3741c5d8f47748e4c
diff --git a/src/main/java/net/onrc/onos/core/topology/TopologyImpl.java b/src/main/java/net/onrc/onos/core/topology/TopologyImpl.java
index e6e6763..81f3041 100644
--- a/src/main/java/net/onrc/onos/core/topology/TopologyImpl.java
+++ b/src/main/java/net/onrc/onos/core/topology/TopologyImpl.java
@@ -157,7 +157,7 @@
             return null;
         }
 
-        Link link = links.get(TopologyElement.TYPE_PACKET);
+        Link link = links.get(TopologyElement.TYPE_PACKET_LAYER);
         if (link != null) {
             // return packet link
             return link;