Add push VLAN treatment and use it in BgpRouter groups

Change-Id: I8c241fd776cdddd77969413736bd786c0d5a4828
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 aa5af74..499e9e7 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
@@ -300,6 +300,11 @@
         }
 
         @Override
+        public Builder pushVlan() {
+            return add(Instructions.pushVlan());
+        }
+
+        @Override
         public Builder transition(FlowRule.Type type) {
             return add(Instructions.transition(type));
         }