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/AnnotationKeys.java b/core/api/src/main/java/org/onlab/onos/net/AnnotationKeys.java
index af74043..de18fc0 100644
--- a/core/api/src/main/java/org/onlab/onos/net/AnnotationKeys.java
+++ b/core/api/src/main/java/org/onlab/onos/net/AnnotationKeys.java
@@ -25,6 +25,17 @@
     private AnnotationKeys() {}
 
     /**
+     * Annotation key for durable links.
+     */
+    public static final String DURABLE = "durable";
+
+    /**
+     * Annotation key for active/inactive links. Links are implicitly
+     * considered active unless explicitly marked otherwise.
+     */
+    public static final String INACTIVE = "inactive";
+
+    /**
      * Annotation key for latency.
      */
     public static final String LATENCY = "latency";