Update RTCDataChannel for bug 1335206 (#2615)
Update RTCDataChannel for bug 1335206 (#2615)

Add an "sctp-sdp-21" feature that indicates support for
the updated format.

Also rearranged a bunch of items to be roughly in
alphabetical order. I may have missed some but really,
it was beyond scope for this change anyway so I'd prefer
not to have to update more of them if I missed any. :)
chrisdavidmills/browser-compat-data,chrisdavidmills/browser-compat-data,mdn/browser-compat-data,teoli2003/browser-compat-data,mdn/browser-compat-data