proc_parse: Introduce @private member into mount_info structure

It will hold auxiliary data associated with mount point. We
will use it for btrfs handling but in future it can be extended.
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

include/proc_parse.h

@@ -126,6 +126,8 @@ struct mount_info {
 	struct mount_info *mnt_master;	/* slave is on master->mnt_slave_list */
 
 	struct list_head postpone;
+
+	void		*private;	/* associated filesystem data */
 };
 
 extern struct mount_info *mnt_entry_alloc();