Enqueue AST_CONTROL_PROGRESS after AST_CONTROL_RINGING when MFC-R2 calls are accepted

(closes issue #18438)
Reported by: mariner7
Tested by: moy


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@299493 65c4cc65-6c06-0410-ace0-fbb531ad65f3