Searching for IP addresses in the arp API endpoint is horribly inefficient

[Morten Brekkevold]

IP-based searches using the arp API endpoint are slow. This is because the `ip` filter is subjected to the default handling of Django REST Framework, which produces Django's horrible default search filter for IP address fields: "HOST(ip) = 'someip'". This casts PostgreSQLs INET datatypes to strings, rendering the ip field index unused as sequential table scans are used instead.

The ip field filter should be handled manually, as it is elsewhere in similar NAV code.

Bonus: We can also handle prefix searches in an improved way when this is done.

[Morten Brekkevold (mbrekkevold)]

fix here: https://nav.uninett.no/hg/nav/rev/7fd8d71cd5da