Explicitly set registerVal max count to 123 to override global limit

[satveerbrar]

Added max_count=123 to the FieldListField for the registerVal field to override the global conf.max_list_count =100

fixes #4573

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.59%. Comparing base (c424205) to head (7817309).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4633      +/-   ##
==========================================
- Coverage   81.61%   81.59%   -0.03%     
==========================================
  Files         359      341      -18     
  Lines       86052    85781     -271     
==========================================
- Hits        70234    69991     -243     
+ Misses      15818    15790      -28     

Files with missing lines	Coverage Δ
scapy/contrib/modbus.py	90.98% <ø> (ø)

... and 273 files with indirect coverage changes