check attribute lengths before reading them

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What does this PR aim to accomplish?:

Netlink attributes are variable-length, so a fixed-size read can run past the payload into the next attribute.

How does this PR accomplish the above?:

Fix the checks.

Link documentation PRs if any are needed to support this PR:

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• I have read the above and my PR is ready for review. Check this box to confirm

This is my first contribution to open source. I have used Claude Code AI and OpenCodex AI to write and review this code and tried to test it as good as I can. But I was not able to cause a crash before and not with this fix. This fix is created after reading #2984 and seeing there are similar places in the same file.

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