Add a callback to sig_pri which is called when sig_pri is going to queue a...

Add a callback to sig_pri which is called when sig_pri is going to queue a control frame on a channel.


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@224491 65c4cc65-6c06-0410-ace0-fbb531ad65f3