fix: protect against bogus negative timestamps in kernel messages (Closes #4526)

[jeff-zed]

Description

This PR fixes an issue where kernel log messages can have negative timestamps, resulting in log entries with timestamps showing dates like "1969-12-31 11:59:59" (Unix epoch -1).

The fix adds validation in getKernelMsg() to check if the kernel message timestamp has a negative Unix timestamp. When detected, it falls back to using the current time instead of the invalid timestamp, ensuring accurate and meaningful log entries.

Fixes: #4526

How to test and validate this PR

make run

Changelog notes

Fixed kernel log entries showing incorrect timestamps (1969 dates) when kernel messages contain negative timestamp values. Kernel logs now use current time as fallback for invalid timestamps.

PR Backports

• 14.5-stable: To be backported (logging accuracy is important for debugging)
• 13.4-stable: To be backported (logging accuracy is important for debugging)

Checklist

• [x] I've provided a proper description
• [x] I've added the proper documentation
• [ ] I've tested my PR on amd64 device
• [ ] I've tested my PR on arm64 device
• [x] I've written the test verification instructions
• [x] I've set the proper labels to this PR

I do not have an amd64 device or a "standard" (non-Apple) arm64 device.

And the last but not least:

• [x] I've checked the boxes above, or I've provided a good reason why I didn't check them.

[eriknordmark]

Is this ready for review and merge? It is still marked as a draft.