Fix net-http tracing's span nesting issue

[st0012]

As mentioned in #1723 (comment), net-http spans should attach to the current span instead of always the top-level transaction.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.42%. Comparing base (942f645) to head (dac0bc3).
⚠️ Report is 555 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1796      +/-   ##
==========================================
+ Coverage   98.41%   98.42%   +0.01%     
==========================================
  Files         145      145              
  Lines        8576     8588      +12     
==========================================
+ Hits         8440     8453      +13     
+ Misses        136      135       -1     

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