drivers: wifi: esp_at: changes to scanning

If CONFIG_WIFI_ESP_AT_SCAN_MAC_ADDRESS: mac addr included in
scanning results.
if CONFIG_WIFI_ESP_AT_SCAN_PASSIVE: passive scanning is used instead of
default active scanning.
If CONFIG_WIFI_ESP_AT_SCAN_RESULT_RSSI_ORDERED: scanning response
ordered by RSSI.

Signed-off-by: Jani Hirsimäki <jani.hirsimaki@nordicsemi.no>