rustfmt: format doc comments

[dianpopa]

Reason for This PR

Fixes #1321.

Description of Changes

[Author TODO: add description of changes.]

• This functionality can be added in rust-vmm.

License Acceptance

By submitting this pull request, I confirm that my contribution is made under
the terms of the Apache 2.0 license.

PR Checklist

[Author TODO: Meet these criteria.]
[Reviewer TODO: Verify that these criteria are met. Request changes if not]

• All commits in this PR are signed (git commit -s).
• The issue which led to this PR has a clear conclusion.
• This PR follows the solution outlined in the related issue.
• The description of changes is clear and encompassing.
• Any required documentation changes (code and docs) are included in this PR.
• Any newly added unsafe code is properly documented.
• Any API changes follow the Runbook for Firecracker API changes.
• Any user-facing changes are mentioned in CHANGELOG.md.
• All added/changed functionality is tested.

[georgepisaltu]

Nice!

[alindima]

I see that this is still considered an unstable feature. Do we want to merge it as-is and later rollback if we see stability issues? @dianpopa

[dianpopa]

I see that this is still considered an unstable feature. Do we want to merge it as-is and later rollback if we see stability issues? @dianpopa

Unstable features are not merged in stable branches (which we are using). Where did you see that this is still unstable?

[alindima]

I see that this is still considered an unstable feature. Do we want to merge it as-is and later rollback if we see stability issues? @dianpopa

Unstable features are not merged in stable branches (which we are using). Where did you see that this is still unstable?

I was referring to the rustfmt docs: https://rust-lang.github.io/rustfmt/?version=v1.4.38&search=#format_code_in_doc_comments

But it seems that the docs are outdated