Fix websocket

We noticed that websocket were broken with this config.

We believe that the translation from old config to new config in [this commit](https://github.com/jitsi/docker-jitsi-meet/commit/130eb551a7666a9a143343e4ac7e707e3d6c6c02#diff-6f9b0c296a7ff789834c1414349f64f956f2b64df6e405fd45f62c6a11edad3fL34) didn't translate it well.

We are actually wondering what does private stands for in this context.

With this change, we can confirm that wss works again as expected.