Client cannot decide destination/port in SETUP

Submitted by Xavier Claessens @xclaesse

Link to original bug (#770954)

Description

Currently the mcast address is allocated from the address pool on DESCRIBE, and only one mcast group is supported. So if a client asks for a specific destination/port in SETUP, default_configure_client_transport() will call gst_rtsp_stream_reserve_address() and will return an error.