"Logic" in iplog_history cleanup

[dwlfrth]

Admins relies on iplog (with _history and _archive) to have an history of ip <-> mac correlation. Keeping too much of records (actually records are deleted according to their "age") will make admin interface slow on some operations. A lot of the content of iplog is leases from reg / isol subnets, which are less "important".

We need to rework cleanup so that reg / isol subnet entries are deleted sooner than others which will allow to keep more "important" data.

[dwlfrth]

This needs some additions to the DB schema to store the interface and/or the network type for each given lease. Also see for the possibility of integrating this feature with the upcoming pfdhcp