Some functions in lib/libc/net were disabled on MINIX3 only, but with
a few added header files they build just fine, even though some of
them rely on system functionality that has not yet been implemented.
Since the functionality is unlikely to be used in practice (because
it typically requires the use of protocol families that themselves are
not yet supported, such as IPv6), already enabling it right now helps
in building packages that rely on the functionality being present at
compile time, while not posing any practical risk of breaking the same
packages at run time.
Change-Id: Idee8e3963c9e300bde9575429f0e77b0565acaef
7ecc6a9247