Provide support for v21 SCTP offer spec

[dlukyanyuk]

According https://bugs.chromium.org/p/webrtc/issues/detail?id=9484 new versions of Chrome are sending new offer format and answer cannot be generated.

For example, for RemoteDescription with info
m=application 54111 UDP/DTLS/SCTP webrtc-datachannel a=sctp-port:5000
pc.CreateAnswer does not produce any result - no error, no answer

Similiar issue for node implementation - node-webrtc/node-webrtc#483

[uumaro]

Do you know, is this just a matter of using a newer version of Chromium to base libwebrtc off of?

[dlukyanyuk]

This occurs when one client uses go-webrtc library and another client uses browser (or mobile app) with newer version of Chromium.

[arlolra]

Do you know, is this just a matter of using a newer version of Chromium to base libwebrtc off of?

Yeah, looks like node-webrtc fixed this by bumping to branch-heads/70