Change ringt (ring timeout) styles to be consistent across chan_dahdi.

(closes issue #15684)
Reported by: alecdavis
Patches: 
      chan_dahdi.bug15684.diff2.txt uploaded by alecdavis (license 585)
Tested by: alecdavis


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@222652 65c4cc65-6c06-0410-ace0-fbb531ad65f3