Improve the data-channels example

[philipch07]

Description

Improves the data-channels example so hopefully it's clear for newcomers (such as myself) to pick up on what's going on!

Reference issue

I was using it to test my SCTP RACK impl, but had some issues figuring out what exactly was going on. Fortunately it seems to work fine.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.80%. Comparing base (7d8a700) to head (1d1fbc0).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3251      +/-   ##
==========================================
- Coverage   82.87%   82.80%   -0.08%     
==========================================
  Files          80       80              
  Lines       11196    11196              
==========================================
- Hits         9279     9271       -8     
- Misses       1498     1504       +6     
- Partials      419      421       +2     

Flag	Coverage Δ
go	82.80% <ø> (-0.08%)	⬇️

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[JoeTurki]

Thanks