Value Types: remove unnecessary prefixes from enumeration constants

Some of our Value types had constants with superflous prefixes
e.g., IpProtocol.IP_PROTO_TCP instead of IpProtocol.TCP

This commit removes those
diff --git a/test_data/of13/flow_add.data b/test_data/of13/flow_add.data
index 854c908..0766375 100644
--- a/test_data/of13/flow_add.data
+++ b/test_data/of13/flow_add.data
@@ -88,7 +88,7 @@
         factory.buildMatch()
             .setMasked(MatchField.IN_PORT, OFPort.of(4), OFPort.of(5))
             .setExact(MatchField.ETH_TYPE, EthType.IPv6)
-            .setExact(MatchField.IP_PROTO, IpProtocol.IP_PROTO_TCP)
+            .setExact(MatchField.IP_PROTO, IpProtocol.TCP)
             .setMasked(MatchField.IPV6_SRC, 
                        IPv6Address.of(0x1CCAFE1CB1101C00l, 0x0028000000000000l),
                        IPv6Address.of(0xFFFFFFFFFFF0FFFFl, 0x1C2C3C0000000000l))