slirp: fix build on mingw32

in_addr_t isn't available on mingw32.  Just use an unsigned long instead.  I
considered typedef'ing in_addr_t on mingw32 but this would potentially be
brittle if mingw32 did introduce the type.

Cc: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
diff --git a/slirp/main.h b/slirp/main.h
index bf601e2..1f3b84d 100644
--- a/slirp/main.h
+++ b/slirp/main.h
@@ -31,7 +31,7 @@
 extern u_int curtime;
 extern fd_set *global_readfds, *global_writefds, *global_xfds;
 extern struct in_addr loopback_addr;
-extern in_addr_t loopback_mask;
+extern unsigned long loopback_mask;
 extern char *username;
 extern char *socket_path;
 extern int towrite_max;