Make one RTPTransport in sip_audio_session.py and keep re-using it, also read ICE settings from config for it

darcs-hash:20081218174133-58103-92e6980ed711255dcde8633ecb870870af31d82d
darcs is available as debian package

darcs-hash:20081219112927-58252-7bdd947008d9ded83a44bd701853e32996b6884b