Invalidate stale wirelen after packet edits

[guedou]

Attempt to fix #4501

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.14%. Comparing base (e2e35c0) to head (afe8b1d).

Files with missing lines	Patch %	Lines
scapy/packet.py	66.66%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5219   +/-   ##
=======================================
  Coverage   81.14%   81.14%           
=======================================
  Files         393      393           
  Lines       98325    98331    +6     
=======================================
+ Hits        79786    79795    +9     
+ Misses      18539    18536    -3     

Files with missing lines	Coverage Δ
scapy/packet.py	84.88% <66.66%> (-0.08%)	⬇️

... and 6 files with indirect coverage changes

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