f2fs: fix to avoid dirent corruption

As Al reported in link[1]:

f2fs_rename()
...
	if (old_dir != new_dir && !whiteout)
		f2fs_set_link(old_inode, old_dir_entry,
					old_dir_page, new_dir);
	else
		f2fs_put_page(old_dir_page, 0);

You want correct inumber in the ".." link.  And cross-directory
rename does move the source to new parent, even if you'd been asked
to leave a whiteout in the old place.

[1] https://lore.kernel.org/all/20231017055040.GN800259@ZenIV/

With below testcase, it may cause dirent corruption, due to it missed
to call f2fs_set_link() to update ".." link to new directory.
- mkdir -p dir/foo
- renameat2 -w dir/foo bar

[ASSERT] (__chk_dots_dentries:1421)  --> Bad inode number[0x4] for '..', parent parent ino is [0x3]
[FSCK] other corrupted bugs                           [Fail]

Fixes: 7e01e7ad ("f2fs: support RENAME_WHITEOUT")
Cc: Jan Kara <jack@suse.cz>
Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Chao Yu <chao@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/namei.c

@@ -1105,7 +1105,7 @@ static int f2fs_rename(struct mnt_idmap *idmap, struct inode *old_dir,
 	}
 
 	if (old_dir_entry) {
-		if (old_dir != new_dir && !whiteout)
+		if (old_dir != new_dir)
 			f2fs_set_link(old_inode, old_dir_entry,
 						old_dir_page, new_dir);
 		else