Sketching out what link-state addition would look like; quite easy until we get to the distributed store.
Added unit tests to provide durable-nondurable transitions.
FIxed issue where link could be accidentally activated.
Renamed parameter.

Change-Id: I8aa19a6583ec50dbf28769995f0a8ea9be9a4daa
diff --git a/core/api/src/main/java/org/onlab/onos/net/link/DefaultLinkDescription.java b/core/api/src/main/java/org/onlab/onos/net/link/DefaultLinkDescription.java
index fc3f335..986eb0a 100644
--- a/core/api/src/main/java/org/onlab/onos/net/link/DefaultLinkDescription.java
+++ b/core/api/src/main/java/org/onlab/onos/net/link/DefaultLinkDescription.java
@@ -34,9 +34,9 @@
     /**
      * Creates a link description using the supplied information.
      *
-     * @param src  link source
-     * @param dst  link destination
-     * @param type link type
+     * @param src         link source
+     * @param dst         link destination
+     * @param type        link type
      * @param annotations optional key/value annotations
      */
     public DefaultLinkDescription(ConnectPoint src, ConnectPoint dst,
@@ -64,9 +64,10 @@
 
     @Override
     public String toString() {
-        return MoreObjects.toStringHelper("Link").add("src", src())
-                                .add("dst", dst())
-                                .add("type", type()).toString();
+        return MoreObjects.toStringHelper(this)
+                .add("src", src())
+                .add("dst", dst())
+                .add("type", type()).toString();
     }
 
 }