while trying to implement addTrack in adapter I ran into the issue that I could not create RTCRtpSender with a null transport.
https://draft.ortc.org/#rtcrtpsender-operation*
Should that be allowed? setTransport could later be used to set the transport.

(for adapter i'll probably just create the ice gatherer, ice transport and dtls transport during addTrack. Seems wrong in terms of semantics but... this is 1.0 and so I am getting used to things feeling wrong)