Kernel: T5887: update Linux Kernel to v6.6.87

[c-po]

Change summary

Upgrade Linux Kernel to latest bugfix version

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

Related Task(s)

• https://vyos.dev/T5887

Related PR(s)

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly

[github-actions]

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[Copilot]

Pull Request Overview

This PR updates the Linux Kernel version in the configuration to the latest bugfix release, 6.6.87, to address known issues.

• Updated the kernel_version in data/defaults.toml to "6.6.87" from "6.6.79".

[sever-sever]

update Kernel version