wil6210: Fix driver down flow

Stations disconnection is executed as part of wil_reset so no
need to do it in wil_down.
Removal of the disconnect operation will also preserve the lock
of wil->mutex during the whole reset flow and prevent handling of
connect event while resetting.
Set wil_status_resetting in earlier stage in the flow to prevent
double resetting call in case communication with FW fails while
bringing the interface down.

Signed-off-by: Lazar Alexei <qca_ailizaro@qca.qualcomm.com>
Signed-off-by: Maya Erez <qca_merez@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>