Priority calculation not possible without knowing component

[robin-raymond]

https://tools.ietf.org/html/rfc5245#section-4.1.2.1

   priority = (2^24)*(type preference) +
              (2^8)*(local preference) +
              (2^0)*(256 - component ID)

The trouble is that the gatherer will start gathering on construction and reporting candidates. The trouble is the priority cannot be calculated as per recommendation because the component ID is not known upon construction. Associated RTCP based gatherers are passed into the start method for a transport created by "createAssociatedTransport()" but the gatherer is not specifically an RTCP based gatherer.

[aboba]

One way to fix this would be to add a .createAssociatedGatherer() method to the IceGatherer, which would return an IceGatherer object with a component attribute of RTCP.

partial interface RTCIceGatherer {
    readonly    attribute RTCIceComponent component;
    RTCIceGatherer createAssociatedGatherer ();
};