win32: avoid mixing SOCKET and file descriptor space

Until now, a win32 SOCKET handle is often cast to an int file
descriptor, as this is what other OS use for sockets. When necessary,
QEMU eventually queries whether it's a socket with the help of
fd_is_socket(). However, there is no guarantee of conflict between the
fd and SOCKET space. Such conflict would have surprising consequences,
we shouldn't mix them.

Also, it is often forgotten that SOCKET must be closed with
closesocket(), and not close().

Instead, let's make the win32 socket wrapper functions return and take a
file descriptor, and let util/ wrappers do the fd/SOCKET conversion as
necessary. A bit of adaptation is necessary in io/ as well.

Unfortunately, we can't drop closesocket() usage, despite
_open_osfhandle() documentation claiming transfer of ownership, testing
shows bad behaviour if you forget to call closesocket().

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Message-Id: <20230221124802.4103554-15-marcandre.lureau@redhat.com>

include/sysemu/os-win32.h

@@ -166,10 +166,10 @@ static inline void qemu_funlockfile(FILE *f)
 }
 
 /* Helper for WSAEventSelect, to report errors */
-bool qemu_socket_select(SOCKET s, WSAEVENT hEventObject,
+bool qemu_socket_select(int sockfd, WSAEVENT hEventObject,
                         long lNetworkEvents, Error **errp);
 
-bool qemu_socket_unselect(SOCKET s, Error **errp);
+bool qemu_socket_unselect(int sockfd, Error **errp);
 
 /* We wrap all the sockets functions so that we can
  * set errno based on WSAGetLastError()