Fix regression in RSN pre-authentication candidate list generation

Fix regression in RSN pre-authentication candidate list generation

Processing of the scan results for RSN pre-authentication candidates
was moved to happen before the network was selected. This resulted in
all candidates being dropped due to no SSID having been configured.
Fix this by moving the processing to happen after the network has
been selected. Since the raw scan results are not available at that
point, use the BSS table instead of scan results to fetch the
information.