recent changes in 93c0742 reduced the msize returned by the server: this is still valid in 9p but not what the suite expected.

we can't call unlinkat with `.' as path, so the hackish solution (but also the only viable one I can see) is to unlinkat ../<dirname>. Furthermore, calling unlinkat(f->dir->fd, f->fpath) was incorrect because f->dir->fd already points to the directory.