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
Merge branch 'master' of github.com:floodlight/loxigen
Merge into master from pull request #86:
Remove unnecessary prefixes from Value Type constants (https://github.com/floodlight/loxigen/pull/86)