9pfs: include linux/limits.h for XATTR_SIZE_MAX

linux/limits.h should be included for the XATTR_SIZE_MAX definition used
by v9fs_xattrcreate.

Fixes: 3b79ef2c ("9pfs: limit xattr size in xattrcreate")
Signed-off-by: Dan Robertson <dan@dlrobertson.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Message-Id: <20200515203015.7090-2-dan@dlrobertson.com>
Signed-off-by: Greg Kurz <groug@kaod.org>

hw/9pfs/9p.c

@@ -28,6 +28,7 @@
 #include "sysemu/qtest.h"
 #include "qemu/xxhash.h"
 #include <math.h>
+#include <linux/limits.h>
 
 int open_fd_hw;
 int total_open_fd;