nfattr_parse_nested always returns success. So we don't need such
checking. It's unlikely that nfattr_parse would return something
different than 0 in the future, if that day comes for whatever reason we
could get the checking back.

-- 
The dawn of the fourth age of Linux firewalling is coming; a time of
great struggle and heroic deeds -- J.Kadlecsik got inspired by J.Morris