chan_iax2: nativebridge refactor, missed unlock bridgecallno

........

Merged revisions 391143 from http://svn.asterisk.org/svn/asterisk/branches/1.8
........

Merged revisions 391148 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@391154 65c4cc65-6c06-0410-ace0-fbb531ad65f3