Fix inconsistencies with Pion twcc.go

[kraigher]

This PR fixes a number of inconsistencies with twcc.go in Pion. I have no idea of how it is supposed to work just that it is not the same so use your own judgement when merging.

[melekes]

👍

[codecov]

Codecov Report

Merging #10 (3bf6f6f) into main (e8a4283) will decrease coverage by 0.06%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main      #10      +/-   ##
==========================================
- Coverage   30.82%   30.76%   -0.07%     
==========================================
  Files          32       32              
  Lines        4522     4522              
  Branches     1186     1185       -1     
==========================================
- Hits         1394     1391       -3     
- Misses       2569     2571       +2     
- Partials      559      560       +1     

Impacted Files	Coverage Δ
src/twcc/twcc_test.rs	61.21% <ø> (-0.13%)	⬇️
src/nack/generator/generator_stream.rs	86.95% <0.00%> (-2.18%)	⬇️
src/lib.rs	7.92% <0.00%> (-0.01%)	⬇️

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[k0nserv]

Thanks @kraigher!