[MV-473] Fix bug when connecting two mobile devices

[graszka22]

What happens:

• mobile adds tracks
• mobile sends join event
• server responds with peer accepted event
• before recent backend update, server would send offerData event and trigger the sdp exchange, but now nothing happens anymore A temporary fix is to send renegotiate track event after joining the server. That way the sdp exchange is triggered after joining joining the room. A more proper fix is to add tracks after joining the room but we can't do it easily now due to threading issues on ios.