privsep: Fix capsicum support on the control socket

[rsmarples]

We need getsockopt support for getpeereid.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 8c929685-20a9-45c6-91b0-e3fd8f44b9a3

📥 Commits

Reviewing files that changed from the base of the PR and between a14857d and 8daf0bf.

📒 Files selected for processing (4)

• src/control.c
• src/dhcpcd.c
• src/privsep.c
• src/privsep.h

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Walkthrough

The change adds a Capsicum descriptor-rights helper, uses it for privileged control-socket setup, and changes interface-specific fallback behavior after EACCES.

Changes

Control socket handling

Layer / File(s)	Summary
Descriptor-rights helper src/privsep.h, src/privsep.c	Declares and implements ps_rights_limit_fd_getsockopt(int). The helper applies read, write, event, accept, getsockopt, and fcntl rights, while ignoring ENOSYS.
Socket setup and fallback src/control.c, src/dhcpcd.c	Privileged socket setup uses the new helper. Interface-specific fallback retries with AF_UNSPEC only when the initial failure is not EACCES.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to 8daf0

The change is localized and no actionable merge-blocking risk remains after normal checks and review.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the capsicum support fix for the control socket, which matches the main changes.
Description check	✅ Passed	The description directly explains the added getsockopt support required by getpeereid.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch capsicum

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