dcerpc: only commit accepted contexts on server side

[gpotter2]

Alternative PR to #5139

closes #5139

[codecov]

Codecov Report

❌ Patch coverage is 95.23810% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 81.17%. Comparing base (22d3930) to head (a81c03d).
⚠️ Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
scapy/layers/dcerpc.py	94.44%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5196      +/-   ##
==========================================
+ Coverage   80.87%   81.17%   +0.30%     
==========================================
  Files         393      393              
  Lines       98082    98092      +10     
==========================================
+ Hits        79327    79630     +303     
+ Misses      18755    18462     -293     

Files with missing lines	Coverage Δ
scapy/layers/msrpce/rpcserver.py	84.38% <100.00%> (+0.91%)	⬆️
scapy/layers/dcerpc.py	91.38% <94.44%> (+0.06%)	⬆️

... and 23 files with indirect coverage changes

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