vod: set up RTSP stack of new media in an asynchronous way

vod: set up RTSP stack of new media in an asynchronous way

This way, we don't take the httpd lock when holding the vlm lock.
This will allow passing synchronous calls from the RTSP stack to the
VLM (as long as you don't use the old vod module at the same time,
which you can't anyway).