Fix traffic metrics

[Menduist]

Thanks @alrevuelta for the report

The incoming bandwidth was completely off (it took the maximum message size instead of the actual one)

[codecov]

Codecov Report

Merging #879 (016e82e) into unstable (bac754e) will increase coverage by 0.09%.
The diff coverage is n/a.

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable     #879      +/-   ##
============================================
+ Coverage     84.08%   84.17%   +0.09%     
============================================
  Files            86       87       +1     
  Lines         14957    15085     +128     
============================================
+ Hits          12576    12698     +122     
- Misses         2381     2387       +6     

Impacted Files	Coverage Δ
libp2p/stream/chronosstream.nim	76.28% <ø> (ø)

... and 12 files with indirect coverage changes

[alrevuelta]

Indeed it works now, thanks!

Image showing before/after fix. Before, nim-libp2p metrics differed from cadvisor (same pattern but amplified). After 14:05 (see time axis), I deployed with the fix in this PR and the bandwidths now match.

(Running nwaku)