[Libguestfs] [PATCH nbdkit v2] Add support for AF_VSOCK.

[Richard W.M. Jones]

v1 was discussed here:
https://www.redhat.com/archives/libguestfs/2019-October/thread.html#00100

v2:

 - Bind to VMADDR_CID_ANY (instead of HOST) and update the
   documentation accordingly.

 - Don't bother with SOCK_CLOEXEC fallback path that can
   never be used.

Rich.