Fix WSAEADDRINUSE EADDRINUSE mismatch.

* src/w32-sock-nonce.inc.h (EADDRINUSE): Avoid redefining.
* src/assuan-socket.c (_assuan_sock_bind): Set error to EADDRINUSE.

With the latest mingw-w64 EADDRINUSE is defined but to a different
value than WSAEADDRINUSE. We need to use EADDRINUSE becuase that is
what applications expect.

• Signed-off-by: Werner Koch <wk@gnupg.org>