namei: store seq numbers in nd->stack[]

we'll need them for unlazy_walk()
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/namei.c

@@ -508,6 +508,7 @@ struct nameidata {
 		void *cookie;
 		const char *name;
 		struct inode *inode;
+		unsigned seq;
 	} *stack, internal[EMBEDDED_LEVELS];
 };
 
@@ -1577,6 +1578,7 @@ static int pick_link(struct nameidata *nd, struct path *link,
 	last->link = *link;
 	last->cookie = NULL;
 	last->inode = inode;
+	last->seq = seq;
 	return 1;
 }