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/DefaultTrafficTreatment.java b/core/api/src/main/java/org/onosproject/net/flow/DefaultTrafficTreatment.java
index f20d6cc..75f7f7f 100644
--- a/core/api/src/main/java/org/onosproject/net/flow/DefaultTrafficTreatment.java
+++ b/core/api/src/main/java/org/onosproject/net/flow/DefaultTrafficTreatment.java
@@ -189,6 +189,10 @@
             return add(Instructions.modVlanPcp(pcp));
         }
 
+        public Builder stripVlan() {
+            return add(Instructions.stripVlanId());
+        }
+
         @Override
         public Builder setIpSrc(IpAddress addr) {
             return add(Instructions.modL3Src(addr));