Support unified-plan

[notedit]

firefox supports unified-plan, latest chrome supports unified-plan too.

https://tools.ietf.org/html/draft-roach-mmusic-unified-plan-00

https://bugs.chromium.org/p/chromium/issues/detail?id=799030

[backkem]

Thanks @notedit . Let us know if you have any specific needs for this feature. That allow us to determine the correct priority.

[notedit]

If we have want to support multi MediaStreams or build a SFU, we need this feature.

[notedit]

unified plan is default in chrome m72 now.

[trivigy]

@notedit Any specific parts regarding the unified-plan that you need? Personally I only need the BUNDLE protocol to work according to the unified-plan, and only related to data channels. What about you? I am going to end up fixing whatever is wrong but only related to data channels. If I know what you need, I might try looking into it along the way. Or at the very least it will be documented here for future work.

[notedit]

@trivigy here is the specific https://tools.ietf.org/html/draft-roach-mmusic-unified-plan-00
What i want is that multi streams use one ice transport, it is common in the sfu server, one peer receive multi remote streams through one peerconnection.