* Cleaning/simplifying some buffer bits
1. NACKs are always inserted in order. So, get rid of
bunch of out-of-order handling in there and simplify.
2. For now, removing triggering a key frame from NACKs.
Let subs drive it.
3. Move to 16-bit sequence numbers except for receiver
report handling. Simplify bits about unwrapping sequence
number on all packets.
4. Remove unused code.
* remove unused field
* Separate from ion-sfu
changes:
1. extract pkg/buffer, twcc, sfu, relay, stats, logger
2. to solve cycle import, move ion-sfu/pkg/logger to pkg/sfu/logger
3. replace pion/ion-sfu => ./
reason: will change import pion/ion-sfu/pkg/* to livekit-server/pkg/*
after this pr merged. Just not change any code in this pr, because it
will confused with the separate code from ion-sfu in review.
* Move code from ion-sfu to pkg/sfu
* fix build error for resovle conflict
Co-authored-by: cnderrauber <zengjie9004@gmail.com>
