Correct RTP handling in chan_unistim and fix transfer process broken in previous fix:

- Fixed too early RTP setup with phone, that cause no ringback tone on caller side
- Handle call transfer cancel only in STATE_CALL case (related to ASTERISK-23073)

(Reported by: Németh Tamás, niurkin sil)



git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/11@409761 65c4cc65-6c06-0410-ace0-fbb531ad65f3