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/Instructions.java b/core/api/src/main/java/org/onosproject/net/flow/instructions/Instructions.java
index 7c3c24e..afbae7d 100644
--- a/core/api/src/main/java/org/onosproject/net/flow/instructions/Instructions.java
+++ b/core/api/src/main/java/org/onosproject/net/flow/instructions/Instructions.java
@@ -130,6 +130,14 @@
     }
 
     /**
+     * Strips the VLAN tag if one is present.
+     * @return a L2 modification
+     */
+    public static L2ModificationInstruction stripVlanId() {
+        return new StripVlanInstruction();
+    }
+
+    /**
      * Creates a MPLS label modification.
      * @param mplsLabel to set.
      * @return a L2 Modification