the size of the destination buffer is known in the iax_frame so that code
won't write past the end of the allocated buffer when sending outgoing frames.
(ASA-2007-014)
git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.2@75444 65c4cc65-6c06-0410-ace0-fbb531ad65f3