Add ADIN link and MAC stats metrics

[Davidbick]

What changed?

• Adds 13 fields to the per-port adin_port_stats_* component: MAC drop counters (dropfull, dropfilt), MAC errors (crc, lserr, phye), traffic/flow counts (rxfrm/txfrm/rxbc/txbc/rxmc/txmc), link state (link), and the frame-check denominator (fcfrm).

How does it make Bristlemouth better?

• Adds extra visibility into what the network actually drops and how traffic flows: congestion vs. filtering vs. corruption, control- vs. data-plane volume, authoritative link state.

Where should reviewers focus?

• Payload size: the component grew 8 to 21 fields/port

Checklist

• Add or update unit tests for changed code
• Ensure all submodules up to date. If this PR relies on changes in submodules, merge those PRs first, then point this PR at/after the merge commit
• Ensure code is formatted correctly with clang-format. If there are large formatting changes, they should happen in a separate whitespace-only commit on this PR after all approvals.

[victorsowa12]

LGTM