nixos/network-interfaces: fix typo in networking.fqdn

        option will result in an evaluation error if the hostname is empty or

        no domain is specified.

        Modules that accept a mere `networing.hostName` but prefer a fully qualified

        Modules that accept a mere `networking.hostName` but prefer a fully qualified

        domain name may use `networking.fqdnOrHostName` instead.

      '';

    };