Fix payload_len calculation for DataPacket.

[Splinter1984]

This PR fix pl_len calculation issue for DataPacket of RTPS protocol.
Take into account the size of inlineQoS during payload length calculation.
Closes #4594

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.71%. Comparing base (6f0faf3) to head (06aeab2).
Report is 7 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4545      +/-   ##
==========================================
- Coverage   81.61%   78.71%   -2.91%     
==========================================
  Files         356      331      -25     
  Lines       85545    80350    -5195     
==========================================
- Hits        69819    63246    -6573     
- Misses      15726    17104    +1378     

Files with missing lines	Coverage Δ
scapy/contrib/rtps/common_types.py	95.27% <100.00%> (ø)

... and 282 files with indirect coverage changes