change isdn4k-utils to optional

[David Cantrell]

A random sampling of users at FUDCon Brno 2008 showed that ISDN isn't  
really in use as much in Europe as previously thought.  When I asked  
people at FUDCon, I was met with laughter, much like when you talk  
about ISDN in the United States.

Are there any places out there still where ISDN is still more deployed  
than PPP dial-ups or DSL?  Please comment on https://bugzilla.redhat.com/show_bug.cgi?id=462126

Thanks,

-- 
David Cantrell <dcantrell at redhat.com>
Red Hat / Honolulu, HI