Implement some of the missing Selector and Match Conditions

Work toward ONOS-509

The following match conditions are added/implemented:
  - IPV6_EXTHDR

Also, fixed the match criteria for the optical signal type
to represent unsigned 8 bits integer (per spec).

Change-Id: I925db19cb43c5d9f589c1f090b6a75faabe0a19b
diff --git a/core/api/src/main/java/org/onosproject/net/flow/DefaultTrafficSelector.java b/core/api/src/main/java/org/onosproject/net/flow/DefaultTrafficSelector.java
index aa9405db..f3f3bf8 100644
--- a/core/api/src/main/java/org/onosproject/net/flow/DefaultTrafficSelector.java
+++ b/core/api/src/main/java/org/onosproject/net/flow/DefaultTrafficSelector.java
@@ -280,6 +280,11 @@
         }
 
         @Override
+        public Builder matchIPv6ExthdrFlags(Integer exthdrFlags) {
+            return add(Criteria.matchIPv6ExthdrFlags(exthdrFlags));
+        }
+
+        @Override
         public Builder matchLambda(Short lambda) {
             return add(Criteria.matchLambda(lambda));
         }