This allows the BSS list to be iterated in order of increasing id
to avoid problems with new scans reordering entries. The order on the
wpa_s->bss list changes with most recently updated entries being moved
to the tail of the list while wpa_s->bss_id list maintains its order
with new entries being added to the tail and old entries being removed
when they expire.
Collect information from scan results into a BSS table that will not
expire information as quickly as scan results where every new scan,
no matter for how limited set of channels/SSIDs, clears all old
information.
For now, this is only used for D-Bus BSS added/removed notifications,
but this will likely be extended to be used internally instead of the
scan results to better support partial scans.
