fix(tap): use corrent virtio feature for CSUM offload

[ihciah]

Changes

Enable TUN_F_CSUM when VIRTIO_NET_F_GUEST_CSUM is negotiated.

Reason

Enable TUN_F_CSUM for TAP device means it's user(which is VMM) can handle partially checksumed packets. Since we deliver the data directly from tap to guest, so it becomes a requirement for the driver.

QEMU's implementation:

• https://github.com/qemu/qemu/blob/0f397dcfecc9211d12c2c720c01eb32f0eaa7d23/hw/net/virtio-net.c#L844
• https://github.com/qemu/qemu/blob/0f397dcfecc9211d12c2c720c01eb32f0eaa7d23/net/net.c#L533
• https://github.com/qemu/qemu/blob/0f397dcfecc9211d12c2c720c01eb32f0eaa7d23/net/tap.c#L265
• https://github.com/qemu/qemu/blob/0f397dcfecc9211d12c2c720c01eb32f0eaa7d23/net/tap-linux.c#L232

Cloud-hypervisor's:

• https://github.com/cloud-hypervisor/cloud-hypervisor/blob/1c7997c5c3c0473177f6c4278b9f29896aeb1842/net_util/src/lib.rs#L163

License Acceptance

By submitting this pull request, I confirm that my contribution is made under
the terms of the Apache 2.0 license. For more information on following Developer
Certificate of Origin and signing off your commits, please check
CONTRIBUTING.md.

PR Checklist

• If a specific issue led to this PR, this PR closes the issue.
• The description of changes is clear and encompassing.
• Any required documentation changes (code and docs) are included in this
  PR.
• API changes follow the Runbook for Firecracker API changes.
• User-facing changes are mentioned in CHANGELOG.md.
• All added/changed functionality is tested.
• New TODOs link to an issue.
• Commits meet
  contribution quality standards.

---

• This functionality cannot be added in rust-vmm.

[bchalios]

Hi @ihciah,

Thanks for your contribution! Could you please solve the style issues in the PR, following this: https://github.com/firecracker-microvm/firecracker/blob/main/CONTRIBUTING.md#contribution-quality-standards?

I think what's missing is a body in your commit message.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.37%. Comparing base (a46d1b9) to head (fd1b77a).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4725   +/-   ##
=======================================
  Coverage   84.37%   84.37%           
=======================================
  Files         249      249           
  Lines       27433    27433           
=======================================
  Hits        23147    23147           
  Misses       4286     4286           

Flag	Coverage Δ
5.10-c5n.metal	?
5.10-m5n.metal	84.58% <100.00%> (?)
5.10-m6a.metal	83.87% <100.00%> (-0.01%)	⬇️
5.10-m6g.metal	80.91% <100.00%> (?)
5.10-m6i.metal	84.58% <100.00%> (?)
5.10-m7g.metal	80.91% <100.00%> (ø)
6.1-c5n.metal	84.59% <100.00%> (-0.01%)	⬇️
6.1-m5n.metal	84.58% <100.00%> (ø)
6.1-m6a.metal	83.88% <100.00%> (+<0.01%)	⬆️
6.1-m6i.metal	84.58% <100.00%> (ø)
6.1-m7g.metal	80.91% <100.00%> (ø)

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