Add missing support for "who hung up" to chan_motif.

(closes issue ASTERISK-20671)
Reported by: Matt Jordan
Review: https://reviewboard.asterisk.org/r/2208/
........

Merged revisions 377462 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@377463 65c4cc65-6c06-0410-ace0-fbb531ad65f3