chore: fix relay client burst limit

[cosmoknightt]

The docs claimed the client burst limit defaults to 2MiB, but the actual flag value has been 400MiB since day one. That's a 200x difference which is pretty misleading if you're trying to figure out how much burst capacity clients actually get.

Also fixed the bandwidth per second doc (was 2MiB/s, actually 40MiB/s).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 39.44%. Comparing base (8a5e929) to head (de9e622).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2461      +/-   ##
==========================================
- Coverage   39.46%   39.44%   -0.02%     
==========================================
  Files         550      550              
  Lines       51083    51083              
==========================================
- Hits        20160    20150      -10     
- Misses      28382    28387       +5     
- Partials     2541     2546       +5     

Flag	Coverage Δ
litt-tests	32.99% <ø> (ø)
unit-tests	40.29% <ø> (-0.03%)	⬇️

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