packetbeat/sniffer: allow multiple interface devices to be followed

[efd6]

What does this PR do?

This runs multiple sniffers for each Sniffer, each handling default route
polling as needed independently. All sniffers terminate if any
individual terminates.

Why is it important?

This allows multiple network devices to be followed.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Author's Checklist

• [ ]

How to test this PR locally

Related issues

• Relates [Packetbeat] Offer a config option to select default route interface as 'device' #31905

Use cases

Screenshots

Logs

[elasticmachine]

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• Start Time: 2022-09-20T01:27:43.050+0000

• Duration: 50 min 34 sec

Test stats 🧪

Test	Results
Failed	0
Passed	1709
Skipped	19
Total	1728

💚 Flaky test report

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🤖 GitHub comments

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[mergify]

This pull request is now in conflicts. Could you fix it? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b network_traffic_multiple_sniffers upstream/network_traffic_multiple_sniffers
git merge upstream/main
git push upstream network_traffic_multiple_sniffers

[elasticmachine]

Pinging @elastic/security-external-integrations (Team:Security-External Integrations)

[andrewkroh]

LGTM (I reviewed the last commit 4d7dab6e8213a68ffc507dfe9c66b4b568b5ef48. I left other comments relating to the parent commits in #32732).

[andrewkroh]

With the sniffer also utilizing the done channel as a shutdown signal, I would consider a future refactoring to combine the shutdown signalling into a single context.Context. Like having a ctx that comes down from the beater package that gets cancelled on shutdown and then pass that into this errgroup as its parent.

[efd6]

If this is OK to merge, please also approve the parent PR; I'd like to keep these separate in the history.

[mergify]

This pull request is now in conflicts. Could you fix it? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b network_traffic_multiple_sniffers upstream/network_traffic_multiple_sniffers
git merge upstream/main
git push upstream network_traffic_multiple_sniffers