Update RSVP module with a new SESSION object, docstrings, & tests

[Dizarc]

Description

• Added RSVP SESSION object as per RFC 3209.
• Added docstrings to all the classes/functions inside the RSVP module.
• Expanded Master dissection test to include more objects.
• Created new test for SESSION object.
• Updated two BitFields to IntFields for clarity.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.33%. Comparing base (fbd0956) to head (995b559).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5026      +/-   ##
==========================================
- Coverage   80.34%   80.33%   -0.01%     
==========================================
  Files         386      386              
  Lines       96034    96043       +9     
==========================================
- Hits        77154    77153       -1     
- Misses      18880    18890      +10     

Files with missing lines	Coverage Δ
scapy/contrib/rsvp.py	93.90% <100.00%> (+0.75%)	⬆️

... and 6 files with indirect coverage changes

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[polybassa]

Thanks for the PR, could you please reduce the amount of docstrings to a minimum, since we want to keep the number of changes low, if possible.