netvsp: tune VF and link delays per guest OS version

[erfrimod]

The 1s VF_DEVICE_DELAY and 5s LINK_DELAY_DURATION exist to work around
Linux hv_netvsc limitations. They are unconditionally applied today,
penalizing Windows, FreeBSD, and modern Linux guests that don't need them.

This PR introduces vf_device_delay() and link_delay_duration() helpers
that consult the guest OS ID and return Duration::ZERO
for guests that do not require the respective delays. The VF delay is gated
on Linux < 6.7 (fixed by upstream commit d30fb712); the link delay still
applies to all Linux versions.

• Added logic to set the delay duration based on OS ID.
• Added to inspect output.
• Added tests to verify logic and inspect output.

NOTE: The link delay duration is used to coalesce link state (up/down) notifications over a time frame. Even if it is technically correct to report each update, there could be beneficial side effects to smoothing them out for the Guest. I won't be able to know how each Guest / Application will behave if they start seeing a storm of link flapping that would previously be reported as one notification every 5 seconds.

Testing: TBD

[Copilot]

Pull request overview

This PR makes netvsp guest-aware when applying VF offer and link-change delays, avoiding Linux-specific workarounds for guests that do not need them while preserving conservative behavior when the guest OS is unknown.

Changes:

• Adds helper logic to derive VF and link delay durations from the Hyper-V guest OS ID.
• Stores the computed delays in channel/coordinator state and exposes them via inspect.
• Adds unit/async tests for guest OS delay selection and inspect output.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
vm/devices/net/netvsp/src/lib.rs	Adds guest OS-aware delay helpers, wires computed delays into netvsp coordinator/channel behavior, and exposes delay values through inspect.
vm/devices/net/netvsp/src/test.rs	Adds guest OS ID construction helpers plus tests for delay policy and inspect reporting.