net: Remove IFF_DOWN flag to compatible with Linux/*BSD

[xiaoxiang781216]

Summary

turn off interface by checking IFF_UP flag isn't set: #1838

Impact

improve the compatibility

Testing

internal

[nuttxpr]

[Experimental Bot, please feedback here]

This PR appears incomplete based on the provided description.

Here's why and what's missing:

• Insufficient Detail: The summary and impact sections lack specifics.

  • Summary: While it links a related issue, the PR needs to clearly explain what functional part of the code is changed to achieve turning off the interface when IFF_UP isn't set.
  • Impact: Simply stating "improve the compatibility" is too vague. The PR needs to detail:
    • Which compatibility issues are addressed?
    • Is this backward compatible?
    • Are there any potential side effects for existing users?

• Missing Testing Information: "Internal" testing is not sufficient for a proper review. The PR must include:

  • Specific build host details: OS, CPU architecture, compiler version used.
  • Specific target details: Architecture (simulated or real hardware), board name, and the configuration used.
  • Relevant log snippets: Don't just paste entire logs. Include specific portions that demonstrate the issue before the change and the successful outcome after the change.

To improve this PR:

1. Expand the Summary: Provide a technical explanation of how the change works.
2. Detail the Impact: Be specific about the compatibility improvements, potential user impact, and any other notable effects.
3. Provide Complete Testing Information: Follow the template's guidelines to include all necessary build/target details and focused log snippets.

A well-documented PR makes it easier for reviewers to understand, verify, and ultimately merge your contribution.

[cederom]

Thank you @xiaoxiang781216 :-)

[GUIDINGLI]

LGTM

[fdcavalcanti]

@jerpelea would be possible to backport this commit on 12.7?
The related commit on nuttx-apps was backported, but it seems this has not. This causes issues on our internal CI wifi tests.

Just tested the release with this commit cherry-picked and it solves the problem.

@xiaoxiang781216 any problem on that?

[jerpelea]

@fdcavalcanti please test #14319