Enable mDNS on each selected interface

[abeltrano]

Type

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

Side Effects

• Breaking change
• Non-functional change

Goals

• Ensure mDNS is actually enabled on each selected interface; PR Add system support for mDNS #266 missed the commit that added this.

Technical Details

• Remove duplicate call to mdns_configure.
• Invoke resolvectl mdns <interface> yes
• Add newline in mDNS configuration prompt template.

Test Results

• Tests from prior PR were actually performed with this version of the code.

Reviewer Focus

• None

Future Work

• Global mDNS setting still needs to be configured.

Checklist

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