Persist mDNS per-interface settings across reboots

[abeltrano]

Type

• Bug fix
• Feature addition
• Feature update
• Documentation
• Build Infrastructure

Side Effects

• Breaking change
• Non-functional change

Goals

• Ensure mDNS per-interface enablement persists across reboots.

Technical Details

• Name per-interface drop-in instance directories to match the .network file names as this is a strict requirement. It's not enough to use the [Match] directive since the drop-in file itself won't be processed unless it has a basename prefix matching and existing .network file.
• Add netplan- suffix to ensure drop-in instance directory basename matches that generated by netplan.
• Rename some variables in the bash config script to be more accurate.

Test Results

• Installed netremote-server-XXX.deb package, rebooted, then verified mDNS was enabled on all interfaces, per below status on the local test machine:

And a separate machine scanning for mDNS services showing the manually configured DNS-SD service netremote2._netremote._udp.local:

Reviewer Focus

• None

Future Work

• None (hopefully).

Checklist

• Build target all compiles cleanly.
• clang-format and clang-tidy deltas produced no new output.
• Newly added functions include doxygen-style comment block.