CORD-48 Implementation of hashing Next Objective in OF-DPA driver. Major changes to ensure multi-ONOS-instance group-chain installation.
Also includes:
     Changes to Next Objective that adds metadata field for applications to optionally send auxillary info to drivers
     Changes to Next Objective that allows more explicit modification of the next objective
     Changes to Forwarding Objective and PendingNext to include hashCode() and equals() method
     MplsBosInstruction included in kryo serializer
     GroupKey's byte[] represented as a hex string
     Bug fix in mpls flow installation to report failure in install
     Bug fix in linkUp in SR app to disallow non-masters to modify groups
     Bug fix in ordering of actions in group

Change-Id: I3e7003f55724c2de79589e43e11d05ff4815a81d
diff --git a/core/api/src/main/java/org/onosproject/net/flowobjective/Objective.java b/core/api/src/main/java/org/onosproject/net/flowobjective/Objective.java
index 6ac7a7a..b1d73a7 100644
--- a/core/api/src/main/java/org/onosproject/net/flowobjective/Objective.java
+++ b/core/api/src/main/java/org/onosproject/net/flowobjective/Objective.java
@@ -21,7 +21,7 @@
 import java.util.Optional;
 
 /**
- * Base representation of an flow description.
+ * Base representation of a flow-objective description.
  */
 @Beta
 public interface Objective {
@@ -35,14 +35,30 @@
      */
     enum Operation {
         /**
-         * Adds the objective.
+         * Adds the objective. Can be used for any flow objective. For forwarding
+         * and filtering objectives, existing objectives with identical selector
+         * and priority fields (but different treatments or next) will be replaced.
+         * For next objectives, if modification is desired, ADD will not
+         * do anything - use ADD_TO_EXISTING.
          */
         ADD,
 
         /**
-         * Removes the objective.
+         * Removes the objective. Can be used for any flow objective.
          */
-        REMOVE
+        REMOVE,
+
+        /**
+         * Add to an existing Next Objective. Should not be used for any other
+         * objective.
+         */
+        ADD_TO_EXISTING,
+
+        /**
+         * Remove from an existing Next Objective. Should not be used for any
+         * other objective.
+         */
+        REMOVE_FROM_EXISTING
     }
 
     /**
@@ -129,6 +145,7 @@
          * @return an objective builder
          */
         Builder withPriority(int priority);
+
     }
 
 }