spnego: Implement 'Late Fallback mechanism'

[gpotter2]

• implement SPNEGO Late Fallback

[codecov]

Codecov Report

❌ Patch coverage is 78.18182% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.58%. Comparing base (301dcc8) to head (124ddd7).

Files with missing lines	Patch %	Lines
scapy/layers/spnego.py	78.18%	12 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5093      +/-   ##
==========================================
- Coverage   80.59%   80.58%   -0.01%     
==========================================
  Files         390      390              
  Lines       96829    96858      +29     
==========================================
+ Hits        78035    78053      +18     
- Misses      18794    18805      +11     

Files with missing lines	Coverage Δ
scapy/layers/ntlm.py	81.04% <ø> (ø)
scapy/layers/spnego.py	83.07% <78.18%> (+0.60%)	⬆️

... and 8 files with indirect coverage changes

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