Move NL80211 <-> Ieee80211 adaption code into own source file

[abeltrano]

Type

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

Side Effects

• Breaking change
• Non-functional change

Goals

• Make NL80211 helper code available more broadly.

Technical Details

• Move helpers that convert NL80211 <-> Ieee80211 types to its own (private) source file.

Test Results

• All unit tests pass.

Reviewer Focus

• None

Future Work

• None

Checklist

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