RFC9686 support added

[tomaszmrugalski]

There's RFC9686 that adds address registration mechanism to DHCPv6. It defines two DHCPv6 messages (ADDR-REG-INFORM and ADDR-REG-REPLY) and one DHCPv6 option (ADDR-REG-ENABLE). Covering those is what this PR does.

This includes new UTs. The tests on master currently fail on unrelated changes (test/scapy/layers/dcerpc.uts). So I ran just the DHCPv6 tests (python3 UTscapy.py -t test/scapy/layers/dhcp6.uts -F) and they all passed. This includes several new ones that were added.

This should have no impact on other libs.

Tox/Flake8 says the code is clean.

There are LOTS of pylint warnings in the dhcp6.py file, but AFAICT none related to my new code.

Haven't contributed in ages, so apologies if missed anything. Will gladly update with whatever is needed.

I've squashed the commits.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.59%. Comparing base (a4f958b) to head (aabb0d4).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4694      +/-   ##
==========================================
- Coverage   82.13%   78.59%   -3.54%     
==========================================
  Files         361      336      -25     
  Lines       86830    81636    -5194     
==========================================
- Hits        71319    64164    -7155     
- Misses      15511    17472    +1961     

Files with missing lines	Coverage Δ
scapy/layers/dhcp6.py	65.44% <100.00%> (-20.63%)	⬇️

... and 288 files with indirect coverage changes

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[tomaszmrugalski]

I don't understand the codecov failure.

Couple issues with that report:

1. It says the global coverage (for all files) went down by 3.54%. That doesn't look right. I added 37 lines of production code. That would imply there's only a bit over 1000 lines of code in the whole Scapy project. That doesn't make sense.

2. When I expand the details, it says 100% of the patch was covered.

I'm not sure how to proceed. I'm willing to tweak the patch as needed. Please advise.

[gpotter2]

Not to worry, codecov acts a bit randomly at times.
Thanks for the PR