Just like r318173, which was for outputting IPv6 addresses in tree
pools, implement outputting of IPv6 addresses in the ippool debug list
of hash type pools (ippool -l -d -t hash). Currently IPv6 in ippool tree
type pool handling is mostly implemented.
This continues theseries of commits to remediate ippool.

This will be MFCed with a yet to be committed series of fixes to ippool
after it has been fully remediated.

PR: 218433