[PATCH 2/5] manual: Document error codes missing for 'if_indextoname'

[Florian Weimer]

* Maciej W. Rozycki:

> +@item ENOSYS
> +This function is not implemented.
> +@end table

I think ENOSYS comes from the unused stub, so we don't need to document
it.  The Hurd implementation has an error path for ENOSYS, but that
looks effectively dead (it requires a race condition on the socket
descriptor).

Thanks,
Florian