DCE/RPC - Add more testing

[gpotter2]

• add more tests to DCE/RPC
• fix NTLM server checking of username
• minor smbclient fix
• improve endpoint mapper resilliency

fixes #4926

[codecov]

Codecov Report

❌ Patch coverage is 65.95745% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.15%. Comparing base (2c787cd) to head (1e60f8f).
⚠️ Report is 15 commits behind head on master.

Files with missing lines	Patch %	Lines
scapy/layers/msrpce/rpcclient.py	42.85%	8 Missing ⚠️
scapy/layers/msrpce/rpcserver.py	52.94%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4921      +/-   ##
==========================================
+ Coverage   80.10%   80.15%   +0.05%     
==========================================
  Files         370      370              
  Lines       91733    91759      +26     
==========================================
+ Hits        73482    73553      +71     
+ Misses      18251    18206      -45     

Files with missing lines	Coverage Δ
scapy/config.py	84.74% <100.00%> (+6.31%)	⬆️
scapy/layers/dcerpc.py	90.58% <100.00%> (+0.56%)	⬆️
scapy/layers/ntlm.py	81.32% <100.00%> (+0.05%)	⬆️
scapy/layers/smbclient.py	74.38% <100.00%> (ø)
scapy/tools/UTscapy.py	65.33% <100.00%> (+0.21%)	⬆️
scapy/layers/msrpce/rpcclient.py	57.58% <42.85%> (+0.24%)	⬆️
scapy/layers/msrpce/rpcserver.py	84.57% <52.94%> (-3.43%)	⬇️

... and 5 files with indirect coverage changes

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