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/test/java/org/onosproject/net/flow/DefaultTrafficSelectorTest.java b/core/api/src/test/java/org/onosproject/net/flow/DefaultTrafficSelectorTest.java
index 3fb62a7..68c15ff 100644
--- a/core/api/src/test/java/org/onosproject/net/flow/DefaultTrafficSelectorTest.java
+++ b/core/api/src/test/java/org/onosproject/net/flow/DefaultTrafficSelectorTest.java
@@ -255,6 +255,10 @@
         assertThat(selector, hasCriterionWithType(Type.MPLS_LABEL));
 
         selector = DefaultTrafficSelector.builder()
+                .matchIPv6ExthdrFlags(Criterion.IPv6ExthdrFlags.NONEXT.getValue()).build();
+        assertThat(selector, hasCriterionWithType(Type.IPV6_EXTHDR));
+
+        selector = DefaultTrafficSelector.builder()
                 .matchLambda(shortValue).build();
         assertThat(selector, hasCriterionWithType(Type.OCH_SIGID));