Honor channel's music class when using realtime music on hold.

(closes issue #15051)
Reported by: alexh
Patches:
      15051.patch uploaded by mmichelson (license 60)
Tested by: alexh



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@209197 65c4cc65-6c06-0410-ace0-fbb531ad65f3