[webrtc-stats] RTCCodecStats needs `transportId` and `isRemote` to give it context

taylor-b has just created a new issue for 
https://github.com/w3c/webrtc-stats:

== RTCCodecStats needs `transportId` and `isRemote` to give it context
 ==
An `RTCCodecStats` by itself (if not being actively used to 
send/receive a stream) doesn't have enough context to be useful. I'd 
suggest adding:

- `transportId` - a payload type only makes sense in the context of an
 RTP session, and there's one RTP session per media transport so I 
think this works.
- `isRemote` - is this a codec we're prepared to encode, or decode?

Please view or discuss this issue at 
https://github.com/w3c/webrtc-stats/issues/109 using your GitHub 
account