correct safety comments and documentation in `revocable.rs`

[BennoLossin]

The Revocable type in rust/kernel/revocable.rs is missing an # Invariants section documenting that the value inside of data is valid if and only if is_available is true. This should be properly documented and then used in the appropriate places. Please also document the required usage of RCU.

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This requires submitting a proper patch to the LKML and the Rust for Linux mailing list. Please recall to test your changes (including generating the documentation if changed, running the Rust doctests if changed, etc.), to use a proper title for the commit, to sign your commit under the Developer's Certificate of Origin and to add a Suggested-by: tag, and a Link: tag to this issue. Please see https://docs.kernel.org/process/submitting-patches.html and https://rust-for-linux.com/contributing for details.

[meritissimo1]

Hi guys ✌️

I've submitted a patch that addresses this issue by adding a snippet to the documentation about security invariants for Revocable. You can find it here:

🔗 https://lore.kernel.org/rust-for-linux/20250501005726.744027-1-marcelomoreira1905@gmail.com/T/#u

Happy to hear any feedback! 🙂

In Brazil we say TAMO JUNTO! 🙂

[meritissimo1]

The v2:

[PATCH v2]

Tkss! =)