dumb_socketpair(): generate named socket path more carefully

dumb_socketpair(): generate named socket path more carefully

Windows forces us to use named-path Unix sockets.  Generating a path in the
temporary directory, combining current high-res time and PID, seems like a
less-bad option.

On GitHub, a commenter
[suggested](https://github.com/microsoft/WSL/issues/4240#issuecomment-1010545442)
that it would be better to use
[GetTempFileName](https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-gettempfilenamea)
here. However, that function:

- Only adds 16 bits of time-based random bits,
- Will currently fail if there aren't 14 characters available for the filename,
- Might conceivably generate paths longer than UNIX_PATH_MAX, and
- Offers no other apparent offsetting advantages

Signed-off-by: Daniel Lenski <dlenski@gmail.com>