Captive Portal: re-introduce hash lookup for accounting purposes

[swhite2]

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Describe the problem

Table redirection allowed for constant time lookups, with the migration to pf this was changed to a linear time lookup.

While here, fix a small edge case that kills states for ips flipping primary IPs according to hostwatch. Also make sure to include the set of ipfw keys to "registered addresses" to make sure theyre properly cleaned up from the table

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Describe the proposed solution

Reuse table lookups.

The add_accounting logic now expects the full set of IP addresses associated with a single client to make sure they use the same rulenumber, this allows us to prevent wasting space in the ruleset. del_accounting is unaffected.

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Related issue

#9355