Cleaning up and enhancing driver subsystem and the flow objective subsystem.

Change-Id: Ica600ef1aaa46d19e764cd7a197454a4e0f85a08
diff --git a/core/api/src/main/java/org/onosproject/net/AnnotationKeys.java b/core/api/src/main/java/org/onosproject/net/AnnotationKeys.java
index 8b55fa3..4e9c6e4 100644
--- a/core/api/src/main/java/org/onosproject/net/AnnotationKeys.java
+++ b/core/api/src/main/java/org/onosproject/net/AnnotationKeys.java
@@ -50,6 +50,11 @@
     public static final String PROTOCOL = "protocol";
 
     /**
+     * Annotation key for the device driver name.
+     */
+    public static final String DRIVER = "driver";
+
+    /**
      * Annotation key for durable links.
      */
     public static final String DURABLE = "durable";