Bug 1016277 - If two different apps try to use the 'telephony' channel at the same time both apps can play audio

See bug https://bugzilla.mozilla.org/show_bug.cgi?id=1016277 please.
Mmm, Andrea (:baku) didn't mention that need. If I do that change any higher audio channel (ringer, publicnotification) doesn't play anymore after accepting a either a GSM or a WebRTC call. I'll raise this on bugzilla, please keep an eye on it. On the other hand, I'll remove all the logs and see if Travis goes green. Thanks for your review.