[PATCH] ws2_32: Very minimal support for AF_UNIX.

[Richard W.M. Jones]

This is actually a repost, it was originally posted last year:
https://www.winehq.org/pipermail/wine-devel/2020-September/thread.html#173276

This patch is substantially the same except that I have fixed it so it
compiled against the latest master branch, and also fixed a place
where I was not calculating a structure size correctly.

I did not add tests.  The current socket tests (without this patch)
don't pass for me and I don't understand how to make them work.
However we do run this patch against our NBD server which makes
extensive use of AF_UNIX in its test suite, and everything runs fine
there.

I'd be happy if someone who understands the Wine code base better than
me and wants AF_UNIX support wants to take this over.

Rich.