iwlwifi: mvm: support rtt confidence indication

The range response notification API has changed to add a value that
indicates the confidence of the rtt result.
Support the new API and print the rtt confidence for debug.

Signed-off-by: Avraham Stern <avraham.stern@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>