Bluetooth: Make EIR_AdvertisingInterval variable length

[antoniovazquezblanco]

Checklist:

• If you are new to Scapy: I have checked CONTRIBUTING.md (esp. section submitting-pull-requests)
• I squashed commits belonging together
• I added unit tests or explained why they are not relevant
• I executed the regression tests (using cd test && ./run_tests or tox)
• If the PR is still not finished, please create a Draft Pull Request

This should fix #4625

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.11%. Comparing base (8f9c7a6) to head (0f40f90).
Report is 5 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4711   +/-   ##
=======================================
  Coverage   82.11%   82.11%           
=======================================
  Files         361      361           
  Lines       86908    86908           
=======================================
  Hits        71365    71365           
  Misses      15543    15543           

Files with missing lines	Coverage Δ
scapy/layers/bluetooth.py	90.39% <ø> (ø)

... and 12 files with indirect coverage changes

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[gpotter2]

Thanks for the PR & sorry for the delay !