Allow NextObjective to refer to another NextObjective by NextId

Change-Id: I4bc5381be8241ddd765668275f02f795ba06a632
(cherry picked from commit 7fbd2b167ac2a8981255dc17aa53b2ba93073018)
(cherry picked from commit f261d5cbaf8e936b5e3b2f0c55d8e9e698922d2d)
diff --git a/core/api/src/main/java/org/onosproject/net/flowobjective/NextTreatment.java b/core/api/src/main/java/org/onosproject/net/flowobjective/NextTreatment.java
new file mode 100644
index 0000000..af849a2
--- /dev/null
+++ b/core/api/src/main/java/org/onosproject/net/flowobjective/NextTreatment.java
@@ -0,0 +1,43 @@
+/*
+ * Copyright 2018-present Open Networking Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.onosproject.net.flowobjective;
+
+/**
+ * Represents next action in the NextObjective.
+ */
+public interface NextTreatment {
+    /**
+     * Types of next action.
+     */
+    enum Type {
+        /**
+         * The next action is specified by a TrafficTreatment.
+         */
+        TREATMENT,
+
+        /**
+         * The next action is specified by an Integer next id.
+         */
+        ID
+    }
+
+    /**
+     * Type of this next action.
+     *
+     * @return type
+     */
+    Type type();
+}