wl12xx: Unset bssid filter, ssid and bssid from firmware on disassoc

On the disassociation event from the mac80211, the wl12xx driver does not
clear the chipset configuration related to the AP - i.e. it does not perform
a DISCONNECT and then a JOIN with zero SSID and dummy BSSID. Also, it does not
unset the BSSID filter.

Often this is not a problem, as the above is performed upon entering idle
state. But if a scenario arises where a new association is attempted without
cycling through idle state, the new association will fail.

Fix this by resetting the firmware state on disassociation.

Signed-off-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Reviewed-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>