Fix deadlock issue in chan_zap with libss7 due to channel variables being set...

Fix deadlock issue in chan_zap with libss7 due to channel variables being set with the channel pvt lock being held. #12512

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@114776 65c4cc65-6c06-0410-ace0-fbb531ad65f3