vfs: take mnt_master to struct mount

make IS_MNT_SLAVE take struct mount * at the same time

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/mount.h b/fs/mount.h
index e4ecf59..7071d8f 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -19,6 +19,8 @@
 #endif
 	struct list_head mnt_mounts;	/* list of children, anchored here */
 	struct list_head mnt_child;	/* and going through their mnt_child */
+	/* yet to be moved - up to mnt_slave */
+	struct vfsmount *mnt_master;	/* slave is on master->mnt_slave_list */
 };
 
 static inline struct mount *real_mount(struct vfsmount *mnt)