The "dahdi show channels" CLI command still reports the DNID of the
previous call even if the call is already hang up.  The "dahdi show
channels" command of older releases clear the DNID once the channel is
hang up.

Regression from the sig_analog/sig_pri extraction from chan_dahdi.

(closes issue #17623)
Reported by: klaus3000
Patches:
      issue17623.patch uploaded by rmudgett (license 664)
Tested by: rmudgett


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@278777 65c4cc65-6c06-0410-ace0-fbb531ad65f3