v1.7.8
SFU: Register the ssrc-audio-level RTP extension (#373)
All major browser negotiate this. Adding it to ion-sfu means it will
get passed on to ion-avp, which can then do active speaker detection.
I noticed TransportCCURI was video only, and this one is audio only, so
I split the registration into two loops.
Updates pion/sdp dependency to 3.0.4