Add FD support for isotpscan

[polybassa]

Checklist:

• If you are new to Scapy: I have checked CONTRIBUTING.md (esp. section submitting-pull-requests)
• I squashed commits belonging together
• I added unit tests or explained why they are not relevant
• 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

fixes #xxx

[codecov]

Codecov Report

Attention: Patch coverage is 51.61290% with 15 lines in your changes missing coverage. Please review.

Project coverage is 81.22%. Comparing base (bd7f2a3) to head (30f23ba).

Files with missing lines	Patch %	Lines
scapy/contrib/isotp/isotp_native_socket.py	50.00%	14 Missing ⚠️
scapy/contrib/isotp/isotp_scanner.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4778      +/-   ##
==========================================
- Coverage   81.23%   81.22%   -0.01%     
==========================================
  Files         363      363              
  Lines       88404    88417      +13     
==========================================
+ Hits        71811    71813       +2     
- Misses      16593    16604      +11     

Files with missing lines	Coverage Δ
scapy/contrib/isotp/isotp_scanner.py	87.25% <66.66%> (-0.37%)	⬇️
scapy/contrib/isotp/isotp_native_socket.py	40.33% <50.00%> (-0.85%)	⬇️

... and 3 files with indirect coverage changes

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