w32: include winsock2.h before windows.h

w32: include winsock2.h before windows.h

Recent Fedora complains while compiling ui/sdl.c:

    /usr/x86_64-w64-mingw32/sys-root/mingw/include/winsock2.h:15:2: warning: #warning Please include winsock2.h before windows.h [-Wcpp]

And with this patch we dutifully obey.

Stefan Weil:

Without that patch, windows.h will include winsock.h
(which conflicts with winsock2.h) when compiling sdl.c.

Normally we define WIN32_LEAN_AND_MEAN, and
windows.h won't include winsock.h.

include/ui/sdl2.h and ui/sdl.c undefine that macro,
so the order of the include files is important.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>