feat(igc): add single-queue polling datapath

[ytakano]

Description

This PR adds the first usable single-queue polling datapath for the Intel I225/I226 driver.

It enables the PCIe bus-mastering required for DMA, sets up single-queue TX/RX descriptor rings, and wires the minimal polling path through send(), recv(), can_send(), and capabilities(). It also adds TX reclamation based on TDH/TDT and RX consume/refill handling for the single-queue path.

This change is intentionally limited to the minimal end-to-end datapath. It does not add shell debug commands, NetDevice::debug_dump, IRQ RX buffering, multi-queue support, or checksum offload

Related links

How was this PR tested?

• make clippy
• make x86_64 RELEASE=1
• make check_x86_64

Real-machine smoke test:

• Connected over /dev/ttyUSB0 at 38400
• Ran (reboot) from the Awkernel serial shell
• Confirmed the target rebooted and returned to the shell
• Ran (ifconfig) and confirmed interface enumeration, including the igc-backed interfac

Notes for reviewers

• Review intent is narrow: minimal polling datapath only.
• Files changed are limited to:
  • awkernel_drivers/src/pcie.rs
  • awkernel_drivers/src/pcie/intel/igc.rs
  • awkernel_drivers/src/pcie/intel/igc/igc_defines.rs
• The main runtime-sensitive pieces are:
  • PCIe endpoint/bridge bus-master enablement
  • single-queue TX descriptor submission/reclaim
  • RX descriptor consume/refill
• Observability, IRQ buffering, multi-queue, and checksum offload are intentionally deferred to later PRs.

[Copilot]

Pull request overview

Adds an initial single-queue, polling-based TX/RX datapath for the Intel I225/I226 (igc) PCIe NIC, including DMA/bus-master enablement and minimal NetDevice wiring.

Changes:

• Enable PCIe bus-mastering (device + bridge) needed for DMA.
• Implement single-queue polling TX submission/reclaim and RX consume/refill, wired through send(), recv(), can_send(), and capabilities().
• Add a few igc descriptor constants required for advanced TX descriptors.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
awkernel_drivers/src/pcie.rs	Enables BUS_MASTER (and forwarding bits on bridges) so endpoints can DMA through bridges.
awkernel_drivers/src/pcie/intel/igc.rs	Implements single-queue polling TX/RX datapath and integrates with the NetDevice trait.
awkernel_drivers/src/pcie/intel/igc/igc_defines.rs	Adds constants for advanced TX descriptor encoding (DTYP + PAYLEN shift).

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