feat: add ioctl flags in linux/if_tun.h

[wlynxg]

Description

Add ioctl flags from linux/if_tun.h

Sources

https://github.com/torvalds/linux/blob/d3d1556696c1a993eec54ac585fe5bf677e07474/include/uapi/linux/if_tun.h#L31

Checklist

• Relevant tests in libc-test/semver have been updated
• No placeholder or unstable values like *LAST or *MAX are
  included (see #3131)
• Tested locally (cd libc-test && cargo test --target mytarget);
  especially relevant for platforms that may not be checked in CI

[rustbot]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @tgross35 (or someone else) some time within the next two weeks.

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[tgross35]

This LGTM. Could you please squash the "update codestyle" commits into their previous commits and rebase to get rid of the merge commit? Or just squash into one if that's easier.