Add option IPv6OnlyPreferred (RFC 8925)

[candlerb]

This DHCP option is needed to support https://github.com/coredhcp/coredhcp/pull/170

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 73.21%. Comparing base (ca2dc33) to head (fb14ecd).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #524      +/-   ##
==========================================
+ Coverage   73.07%   73.21%   +0.13%     
==========================================
  Files          80       80              
  Lines        5059     5073      +14     
==========================================
+ Hits         3697     3714      +17     
+ Misses       1219     1216       -3     
  Partials      143      143              

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[pmazzini]

Don't you want to add parsing for this option as well to avoid having to deal with OptGeneric in the coredhcp code?

[candlerb]

Good point. Helpers added, and tested with a corresponding patched coredhcp.

[candlerb]

I think this is in shape for a recheck now, thanks.

[candlerb]

Many thanks. I'm good for you to merge this, and #525.

[candlerb]

Thank you!