nl80211: Prefer newer scan result over older during duplicate removal

nl80211: Prefer newer scan result over older during duplicate removal

Previously, it was possible for bss_info_handler() to end up dropping a
newer scan result entry if there were two entries with the same BSSID
and SSID (i.e., only frequency was different) and we were not associated
with either. This could happen, e.g., in some P2P use cases where device
discovery may happen on different channels. Fix this by checking the age
of the scan entries as well to prefer the most recent response.

Signed-hostap: Jouni Malinen <j@w1.fi>