Update WPA/RSN IE properly for driver based BSS selection

Update WPA/RSN IE properly for driver based BSS selection

This patch fixes an issue with roaming for drivers that set
WPA_DRIVER_FLAGS_BSS_SELECTION (currently ath6kl). On moving to an AP
with a different BSSID, an EVENT_ASSOC is received and the subsequent
4-way handshake may fail because of a mismatch between the RSN IE in
message 3/4 and in Beacon/Probe Response. This happens only when the APs
use different RSN IE contents and ap_scan is set to 1, since
wpa_supplicant fails to update its cached IEs.

Initial association may fail, too, in case of multiple APs with
the same SSID, since BSSID selection is done by the driver and again
a mismatch could be seen.

Fix these two issues by clearing and updating the cached IEs on
receiving an Association event from the driver. Also, retrieve the
scan results when the new BSS information is not present locally.

Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>