add support for custom datachannel options in janus.js

[sqxieshuai]

No description provided.

[lminiero]

Thanks! I'll have to check if this can cause issues with Janus, as IIRC we do make some assumptions (e.g., ordered=true) in the Janus core too (sctp.c). Have you checked if the custom datachannel options work as expected for you when you use them?

[sqxieshuai]

@lminiero In my business, I use datachannel to send some data that does not depend on reliability, such as heartbeat and speed measurement. After using it for a period of time, no serious problems are found.

[lminiero]

Thanks, merging then! ✌️