|WARNING| net/idpf: add 400G link speed support

[dpdklab at iol.unh.edu]

Test-Label: ai-code-review
Test-Status: WARNING
https://dpdk.org/patch/172209

_AI Code Review_

=== Patch Review: series.patch (via Claude) ===
Review date: 2026-10-28

# DPDK Patch Review

## File: drivers/net/intel/idpf/idpf_ethdev.c

### Summary
This patch adds 400G link speed support to the idpf PMD by adding `RTE_ETH_SPEED_NUM_400G` to the `idpf_supported_speeds[]` array.

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## ERRORS

None identified.

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## WARNINGS

**Missing release notes update**

The patch adds support for a new link speed (400 Gbps), which is a user-visible feature enhancement. This should be documented in the release notes (`doc/guides/rel_notes/release_26_03.rst` or appropriate version).

**Suggested fix:**
Add an entry to the release notes under the PMD changes section:

```rst
* **Updated idpf driver.**

  * Added support for 400 Gbps link speed.
```

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## INFO

None.

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## Review Summary

The code change itself is correct and straightforward. The addition of `RTE_ETH_SPEED_NUM_400G` to the `idpf_supported_speeds[]` array follows the existing pattern and will allow the driver to correctly report 400G link speeds instead of falling back to "Unknown".

The C code style is compliant:
- Proper indentation and formatting
- No forbidden tokens
- Consistent with surrounding code

The only issue is the missing release notes update, which is required for user-visible feature additions according to the DPDK contribution guidelines.

Review-Result: WARNING