change isdn4k-utils to optional

[Peter Robinson]

>> I am not surprised that you have analogue dialup customers. I am very
>> surprised that ISDN dialup still exists. ISDN BRI must have been a
>> massive success in Germany compared to pretty much anywhere else.
>
> I'm surprised that people make so many assumptions about other countries.
> And till I do not understand why it is so unbelievable that there are
> still ISDN dialups.
>
> B.t.w. in the Netherlands the use of ISDN has also been pretty popular
> and I know that there are still new ISDN lines delivered.

They are in Australia as well as they can run over relatively long
distances unlike ADSL.

Also not sure what the difference between dialup ISDN and what is used
by VoIP gateways such as asterisk that used ISDN PRIs for getting out
onto the PSTN.

Peter