Win32: Don't remove const attribute in type casts.

Type casts removing the const attribute are bad because
they hide the fact that the argument remains const.

They also result in a compiler warning (at least with MS-C).

Signed-off-by: Stefan Weil <weil@mail.berlios.de>
diff --git a/net.c b/net.c
index 58d68b5..af9de73 100644
--- a/net.c
+++ b/net.c
@@ -1507,7 +1507,7 @@
 {
     NetSocketState *s = vc->opaque;
 
-    return sendto(s->fd, (void *)buf, size, 0,
+    return sendto(s->fd, (const void *)buf, size, 0,
                   (struct sockaddr *)&s->dgram_dst, sizeof(s->dgram_dst));
 }