Make sb-bsd-socket work on common protocols without getprotobyname.

Android doesn't have a working getprotobyname, but even for other
platforms iterating over a small number of predefined protocols is
much faster, and some default installations do not come bundled with
/etc/protocols.
Implement sb-posix:stat using wrappers.

It's not easy to determine the layout of struct stat, and it fails to
do so on Android, sb-unix:stat is implemented with a wrapper which
parses everything on the C side. Just reuse that wrapper for
sb-posix:stat.
Revert "Implement sb-posix:stat using wrappers."

It doesn't fix all the Android problems, just pushes them away.