* Do not send both asb-send-time and twcc.
In single peer connection mode, both extensions are set on the media
engine and both would be negotiated. Unfortunately, pion/webrtc does
not yet support RTPSender.SetParameters() which would allow setting
specific header extensions for the sender. So, check for TWCC enabled
and use it. If not, do abs-send-time if that is enabled.
* check BWE type
* comment
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