Revert some logic for session timers. We do send in-dialog requests that should not have session-timer
require headers, like MESSAGE and REFER. So in the future, only add them on requests and responses
that are related to INVITEs and re-INVITEs.


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@127779 65c4cc65-6c06-0410-ace0-fbb531ad65f3