Tun: add support for Darwin utun interface

[0x-0ddc0de]

Fixes #4049

Darwin creates tunnel interfaces differently than BSD, breaking the existing handling which is based on generic BSD tun. This commit adds a new tunnel layer specific to the Darwin utun interface.

This PR picks up the work after the draft PR #4100 got abandoned 2 years ago.

Checklist:

• [x ] If you are new to Scapy: I have checked CONTRIBUTING.md (esp. section submitting-pull-requests)
• [x ] I squashed commits belonging together
• [x ] I added unit tests or explained why they are not relevant
• [x ] I executed the regression tests (using cd test && ./run_tests or tox)
• If the PR is still not finished, please create a Draft Pull Request

TunTapInterface attempts to handle tunnels in Darwin by following the BSD code path. However, this fails for multiple reasons, including the initial rejection of the interface name beginning with "utun" rather than "tun". This PR adds special-case handling for Darwin.

fixes #4049

[codecov]

Codecov Report

❌ Patch coverage is 51.51515% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.88%. Comparing base (d73bbc1) to head (b1f901b).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
scapy/layers/tuntap.py	51.51%	16 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4816      +/-   ##
==========================================
- Coverage   80.88%   80.88%   -0.01%     
==========================================
  Files         368      368              
  Lines       90211    90231      +20     
==========================================
+ Hits        72969    72983      +14     
- Misses      17242    17248       +6     

Files with missing lines	Coverage Δ
scapy/layers/tuntap.py	76.47% <51.51%> (-6.36%)	⬇️

... and 6 files with indirect coverage changes

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[0x-0ddc0de]

Hi @micolous,
You were a reviewer on the draft PR for this issue. That draft PR got abandoned and I completed the work in this new PR. Are you available to review this PR? Thanks

[0x-0ddc0de]

This PR has been open for a month and I haven't been seeing any new feedback. Is there some kind of additional test that should be added to facilitate things? This is my first time opening PR to this project so I'm not familiar with the maintainers expectations beyond what the docs already mentioned.

[gpotter2]

Hi. Sorry for the delay. I'm basically alone to review dozens of PRs, and I often don't have that much time to allocate to it ^^

It looks fine. Thanks for your work.