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/LinkStore.java b/core/api/src/main/java/org/onlab/onos/net/link/LinkStore.java
index 95962e7..3af4f9f 100644
--- a/core/api/src/main/java/org/onlab/onos/net/link/LinkStore.java
+++ b/core/api/src/main/java/org/onlab/onos/net/link/LinkStore.java
@@ -95,6 +95,16 @@
                                         LinkDescription linkDescription);
 
     /**
+     * Removes the link, or marks it as inactive if the link is durable,
+     * based on the specified information.
+     *
+     * @param src link source
+     * @param dst link destination
+     * @return remove or update link event, or null if no change resulted
+     */
+    LinkEvent removeOrDownLink(ConnectPoint src, ConnectPoint dst);
+
+    /**
      * Removes the link based on the specified information.
      *
      * @param src link source
@@ -103,4 +113,5 @@
      */
     LinkEvent removeLink(ConnectPoint src, ConnectPoint dst);
 
+
 }