nl80211: always accept scan request with the duration set

Accept a scan request with the duration set even if the driver
does not support setting the scan dwell. The duration can be used
as a hint to the driver, but the driver may use its internal logic
for setting the scan dwell.

Signed-off-by: Avraham Stern <avraham.stern@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20201129172929.9491a12f9226.Ia9c5b24fcefc5ce5592537507243391633a27e5f@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>