Add SAE J1939 protocol support to Scapy contrib

[polybassa]

No description provided.

[polybassa]

@BenGardiner Please review.

[codecov]

Codecov Report

❌ Patch coverage is 59.33610% with 98 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.89%. Comparing base (366530e) to head (def7ba4).

Files with missing lines	Patch %	Lines
scapy/contrib/j1939.py	59.33%	98 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4963      +/-   ##
==========================================
+ Coverage   79.51%   79.89%   +0.38%     
==========================================
  Files         381      382       +1     
  Lines       93716    93957     +241     
==========================================
+ Hits        74521    75071     +550     
+ Misses      19195    18886     -309     

Files with missing lines	Coverage Δ
scapy/contrib/j1939.py	59.33% <59.33%> (ø)

... and 46 files with indirect coverage changes

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[BenGardiner]

You're gonna need a _Soft_J1939Socket too I think