fix traffic swap

[aobt]

Using Swap to keep the usingBandWidth swap into lastSecondBandwidth atomically;

otherwise, between Load() and Store(0), usingBandWidth may be added, that will be dropped unexpectedly;

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 51.97%. Comparing base (5cee901) to head (15a6fab).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3188      +/-   ##
==========================================
- Coverage   52.00%   51.97%   -0.04%     
==========================================
  Files         173      173              
  Lines       19354    19352       -2     
==========================================
- Hits        10065    10058       -7     
- Misses       8582     8587       +5     
  Partials      707      707              

Flag	Coverage Δ
unittests	51.97% <100.00%> (-0.04%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
client/daemon/peer/traffic_shaper.go	83.87% <100.00%> (-0.26%)	⬇️

... and 1 file with indirect coverage changes

[jim3ma]

LGTM

[gaius-qi]

LGTM

[gaius-qi]

LGTM