inode_fixup.c: Fix check for directory hard links

inode_fixup.c: Fix check for directory hard links

We shouldn't assume that the attributes are consistent, so we should
check both ways for directory hard links.  Specifically, in the case
where the being-inserted dentry is not marked as a directory but for some
reason it shares an inode number with a dentry marked as a directory, we
want to detect that as a directory hard link.