[webrtc-stats] Metrics for header+padding bytes sent and received (#505)

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

== Metrics for header+padding bytes sent and received ==
bytesSent and bytesReceived is payload only.
A bug in Chrome is to implement them as payload + header and padding. It would be useful to be able to get both pieces of information (total network throughput), and having both would make it easier to roll out the fix in Chrome to update its counters to be payload bytes only, as that would allow applications relying on them to calculate the total themselves and not see a dip when the fix is rolled out.

Please view or discuss this issue at https://github.com/w3c/webrtc-stats/issues/505 using your GitHub account