Fix #4717 & cleanup NTP control

[gpotter2]

fixes #4717

[codecov]

Codecov Report

Attention: Patch coverage is 92.30769% with 1 line in your changes missing coverage. Please review.

Project coverage is 81.03%. Comparing base (0f7b0c0) to head (beaa903).
Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
scapy/layers/ntp.py	92.30%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4791   +/-   ##
=======================================
  Coverage   81.02%   81.03%           
=======================================
  Files         365      365           
  Lines       89068    89024   -44     
=======================================
- Hits        72170    72138   -32     
+ Misses      16898    16886   -12     

Files with missing lines	Coverage Δ
scapy/layers/ntp.py	87.65% <92.30%> (+2.32%)	⬆️

... and 5 files with indirect coverage changes

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