rtspsrc: fix race in state change to paused
When we go to paused, we first flush the connection and then send the pause command. As a result of the flushing, the scheduled paused command can get lost. Wait until the connection is completely flushed and the rtsp task is waiting before issuing the paused or playing request. Fixes https://bugzilla.gnome.org/show_bug.cgi?id=702705