Fix Linux Send Complete Status

[nibanks]

Description

Linux TCP was recently broken when secnetperf was updated to handle send completion errors. This exposed a bug in the platform layer that was always passing up errno incorrectly.

This PR updates the platform abstraction to return the proper status.

Testing

Verified locally on Linux GitHub Codespaces. CI/CD

Documentation

N/A

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.03%. Comparing base (e5aa857) to head (beb4e26).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4538      +/-   ##
==========================================
- Coverage   86.12%   86.03%   -0.10%     
==========================================
  Files          56       56              
  Lines       15520    15520              
==========================================
- Hits        13367    13353      -14     
- Misses       2153     2167      +14     

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