fix corsa pipeline divergence : need to differentiate between write and apply instructions.

Change-Id: I477d27d6e52a8e09744614e5f5aa843dd26331e0
diff --git a/core/api/src/main/java/org/onosproject/net/flow/instructions/L2ModificationInstruction.java b/core/api/src/main/java/org/onosproject/net/flow/instructions/L2ModificationInstruction.java
index 4702266..2a93b45 100644
--- a/core/api/src/main/java/org/onosproject/net/flow/instructions/L2ModificationInstruction.java
+++ b/core/api/src/main/java/org/onosproject/net/flow/instructions/L2ModificationInstruction.java
@@ -53,6 +53,11 @@
         VLAN_PCP,
 
         /**
+         * Strips the vlan.
+         */
+        STRIP_VLAN,
+
+        /**
          * MPLS Label modification.
          */
         MPLS_LABEL,
@@ -273,6 +278,33 @@
         }
     }
 
+    public static final class StripVlanInstruction extends L2ModificationInstruction {
+
+        @Override
+        public L2SubType subtype() {
+            return L2SubType.STRIP_VLAN;
+        }
+
+        @Override
+        public String toString() {
+            return subtype().toString();
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(type(), subtype());
+        }
+
+        @Override
+        public boolean equals(Object obj) {
+            if (this == obj) {
+                return true;
+            }
+
+            return false;
+        }
+    }
+
     /**
      * Represents a VLAN POP modification instruction.
      */