Issue #92: readonly attributes

In the Editor's draft, we have:

partial interface RTCDtlsTransport {
attribute RTCIceTransport transport;
};

partial interface RTCRtpSender {
attribute RTCDTlsTransport transport;
};

partial interface RTCRtpReceiver {
attribute RTCDTlsTransport transport;
};

Should these attributes be readonly? That is what was proposed today in W3C WEBRTC.

If the desire is to change the transports, shouldn't we have a setter to accomplish this?