From: Christian Borntraeger <linux@borntraeger.net>
  
This patch makes isdn_tty HZ aware.
The first change changes 3000 jiffies (now 3 seconds) to 30 seconds according to
the comment.
I dont know, if the second change (schedule_timeout(50);) has to be half a
second but this was the value used in 2.4.