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/TrafficSelector.java b/core/api/src/main/java/org/onosproject/net/flow/TrafficSelector.java
index 1ecab71..7d31b08 100644
--- a/core/api/src/main/java/org/onosproject/net/flow/TrafficSelector.java
+++ b/core/api/src/main/java/org/onosproject/net/flow/TrafficSelector.java
@@ -300,6 +300,14 @@
         public Builder matchMplsLabel(Integer mplsLabel);
 
         /**
+         * Matches on IPv6 Extension Header pseudo-field fiags.
+         *
+         * @param exthdrFlags the IPv6 Extension Header pseudo-field fiags
+         * @return a selection builder
+         */
+        public Builder matchIPv6ExthdrFlags(Integer exthdrFlags);
+
+        /**
          * Matches an optical signal ID or lambda.
          *
          * @param lambda lamda