[webrtc-pc] When is an RTCSctpTransport created and destroyed?

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

== When is an RTCSctpTransport created and destroyed? ==
This should be documented more clearly. Things that aren't obvious to 
me right now:

1. Is the SctpTransport created after applying an offer, or only after
 applying an answer?
2. If the data "m=" section is rejected, does the SctpTransport go 
away? I'd guess yes.
3. If the SCTP port ("a=sctp-port") is changed, and a new SCTP 
association is formed, is a new SctpTransport created to represent 
that association? I'd lean towards "yes".
4. Secondary question: Do we even want to support changing the SCTP 
port? It's not clear we have any use case for this.

Please view or discuss this issue at 
https://github.com/w3c/webrtc-pc/issues/979 using your GitHub account