Machinetracker MAC search performs unnecessary join with Netbios table

[lunkwill42]

Cognate with #235, the Machine tracker MAC search also performs a join with the Netbios table, regardless of whether the user has checked the "netbios" checkbox in the search form (observed in NAV 4.8.5)

The join uses the PostgreSQL OVERLAPS operator to match arp and netbios records on time ranges, and performs quite badly once the number of netbios records grows (which is a good reason to try to switch to using the tsrange data type for tables like arp, cam and netbios in the future - those can be be more efficiently indexed)

[lunkwill42]

These are the offending lines:

nav/python/nav/web/machinetracker/views.py

Lines 265 to 270 in 57b194b

	arp_result = Arp.objects.select_related('netbox').filter(
	end_time__gt=from_time,
	mac__range=(mac_min, mac_max)
	).extra(
	select={'netbiosname': get_netbios_query()},
	).order_by('mac', 'ip', '-start_time')