Fix Azure networking failures on FreeBSD by correcting NIC discovery, interface selection, and platform-specific networking behavior.

[MoeSalah1999]

Proposed Commit Message

On Azure FreeBSD images, cloud-init fails during early networking setup due to a combination of platform mismatches and incorrect assumptions:

- Azure exposes both a Hyper-V synthetic NIC (hn*) and an accelerated VF (mce*) that intentionally share the same MAC address.
- cloud-init assumes MAC addresses uniquely identify interfaces, causing one interface to be silently discarded during enumeration.
- FreeBSD lacked parity with Linux logic that filters Hyper-V accelerated VFs when a synthetic interface is present.
- Interface ordering on FreeBSD was undefined, allowing the VF to be selected as the primary NIC.
- BSD networking code did not fully match the netops API used by cloud-init core.
- Azure ephemeral networking logic hard-failed when DHCP context fields were not populated on non-Linux platforms.

In combination, these issues caused cloud-init to attempt DHCP on the wrong interface, invoke Linux-specific networking operations on FreeBSD, and abort instance initialization.

**Changes Made:**
**1. Tolerate duplicate MAC addresses on FreeBSD**

get_interfaces_by_mac_on_freebsd() now preserves the first discovered interface when duplicate MAC addresses are encountered and logs the event instead of overwriting or failing.

- Maintains the existing Dict[str, str] return contract.
- Prevents loss of the synthetic hn* interface when an accelerated VF shares its MAC.
- Aligns FreeBSD behavior with existing Linux duplicate-MAC tolerance.

**2. Correct FreeBSD device discovery**

get_devicelist() and FreeBSD NIC discovery paths were adjusted to avoid relying on MAC-keyed maps for interface enumeration.

- Ensures all candidate interfaces are discovered on FreeBSD.
- Prevents interface loss due to MAC collisions.
- Keeps Linux and BSD discovery paths separate and appropriate.

**3. Filter Hyper-V accelerated VFs on FreeBSD**

Added FreeBSD parity with existing Linux logic that filters Hyper-V accelerated virtual functions when a synthetic interface is present.

- On Azure FreeBSD:
                 - hn* interfaces are treated as synthetic.
                 - mce* interfaces are treated as accelerated VFs.
- Prevents cloud-init from selecting the VF as the primary interface.
- Mirrors established Linux behavior for Hyper-V environments.

**4. Prefer hn0 as the primary interface on FreeBSD**

Explicitly orders FreeBSD interfaces so that hn0 is preferred when present.

- Reflects Azure platform expectations.
- Ensures deterministic primary NIC selection.
- Avoids reliance on enumeration order or timing.

**5. Fix BSD netops API mismatch**

Updated BsdNetOps.link_down() to accept the family argument expected by the cloud-init netops API.

- Prevents runtime TypeError during network teardown/setup.
- Aligns BSD netops with other platform implementations.
- Does not alter behavior for existing callers.

Fixes GH-6657

Additional Context

Results:

With these changes applied:

• The correct synthetic NIC (hn*) is consistently selected on Azure FreeBSD.
• Duplicate MAC addresses no longer cause interface loss.
• Accelerated VFs are ignored when inappropriate.
• FreeBSD networking uses the correct netops implementation.
• Azure datasource initialization completes successfully.
• No public APIs or existing test expectations are broken.

Scope and Compatibility:

• Changes are limited to FreeBSD and Azure-specific behavior.
• Linux behavior remains unchanged.
• Public helper function return types are preserved.
• All existing unit tests remain valid.

Test Steps

Provided tests in tests/unittests/net/test_net_freebsd.py.

Log Evidence

This change is covered by new FreeBSD-specific unit tests which assert:

• duplicate MAC detection
• preservation of the synthetic hn* interface
• emission of the expected debug log message

Example asserted log output:

                            Duplicate MAC aa:bb:cc:dd:ee:ff found on hn0 and mce0; keeping first

Merge type

• Squash merge using "Proposed Commit Message"
• Rebase and merge unique commits. Requires commit messages per-commit each referencing the pull request number (#<PR_NUM>)

[MoeSalah1999]

Would love to have your opinion on this if possible @blackboxsw

[holmanb]

Thanks for this @MoeSalah1999. Please include logs to show that this works.

[MoeSalah1999]

Thanks for this @MoeSalah1999. Please include logs to show that this works.

Thanks @holmanb for the review. I don’t currently have access to an Azure FreeBSD environment to collect live logs, but I’ve added FreeBSD-specific unit tests that exercise the affected code paths and assert the expected debug logging.

In particular, the tests verify that duplicate MAC addresses are detected, the synthetic hn* interface is preserved, accelerated VFs are filtered, and the corresponding debug logs are emitted. I’ve also referenced the asserted log output in the PR description.

[MoeSalah1999]

CLA check is failing for some reason, even though I have signed the CLA.