mac80211: remove disconnected APs from BSS table

In some cases, after a sudden AP disappearing and reconnection to
another AP in the same ESS, user space gets the old AP in scan
results (cached). User space may decide to roam to that old AP
which will cause a disconnection and longer recovery.
Remove APs that are probably out of range from BSS table.

Signed-off-by: David Spinadel <david.spinadel@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>