When an inital INVITE occurs that contains image media, a channel
is not yet associated with the SIP dialog. The file descriptor
associated with the udptl session needs to be set in
initialize_udptl or in sip_new to account for this scenario.
git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@351233 65c4cc65-6c06-0410-ace0-fbb531ad65f3