- While here, make this compile and work on non-i386:
- Use CMSG_SPACE(), CMSG_LEN(), and CMSG_FIRSTHDR() instead of ignoring
padding between 'struct cmsghdr' and control message payloads.
- Don't initialize the control message before calling recvmsg().
Instead, check that we get a valid control message on return from
recvmsg().
- Use errx() instead of err() for some errors that don't report failures
that set errno.
Requested by: kib (1)
