Remove protocol names, instead use an enum with common protocols

Remove protocol names, instead use an enum with common protocols

The whole protocol name thing is pretty weird. The getprotobyname functions
seem to only specify one mapping for name <-> ids, so all families/types
must use the same values. Plus the values used for the protocols are
standardized by IANA, so are always the same.

So, we drop using names for protocols, intead introducing an enum with
a few commonly availible and used protocols.