ENG-37132: using already computed bodyLen

[puneet-traceable]

Description

Use already computed bodyLen variable

Checklist:

• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• Any dependent changes have been merged and published in downstream modules

[codecov]

Codecov Report

Merging #221 (bc5d4e5) into main (157e76c) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #221   +/-   ##
=======================================
  Coverage   59.20%   59.20%           
=======================================
  Files          55       55           
  Lines        2250     2250           
=======================================
  Hits         1332     1332           
  Misses        859      859           
  Partials       59       59           

Files	Coverage Δ
sdk/instrumentation/bodyattribute/bodyattribute.go	100.00% <100.00%> (ø)

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