This adds a minimal implementation of the "Who Hung Up?" Asterisk 11
work to chan_dahdi.c for the MFC/R2 DAHDI subtech. Given the way that
OpenR2 interfaces with chan_dahdi, it is much harder to expose the
type of protocol information that is available in PRI, SS7, or other
channel technologies.
git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@369190 65c4cc65-6c06-0410-ace0-fbb531ad65f3