MFstable/10 r228371:

MFstable/10 r228371:

This missing MFC fixes PR 199308

r228371 (by jhb):

- Add a test for PR 151758.
- 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)

git-svn-id: svn://svn.freebsd.org/base/stable/9@281314 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f