server: start and stop multiple times
server: start and stop multiple times

Stop listening on the RTSP port when the GSource is removed, so clients
can't connect and the server can be started again.

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=688395

barisdemiray/gst-rtsp-server,hsteinhaus/gst-rtsp-server,surround-io/gst-rtsp-server,barisdemiray/gst-rtsp-server,Lachann/gst-rtsp-server,surround-io/gst-rtsp-server,hsteinhaus/gst-rtsp-server,Lachann/gst-rtsp-server,thaytan/gst-rtsp-server,surround-io/gst-rtsp-server,thaytan/gst-rtsp-server,thaytan/gst-rtsp-server,Lachann/gst-rtsp-server,barisdemiray/gst-rtsp-server,hsteinhaus/gst-rtsp-server