iwlwifi: mvm: Configure EBS scan ratio

This configuration defines the ratio between number of scan iterations
where EBS is involved to those where it is not.
This configuration was left unconfigured due to inaccurate documentation.
Fix documentation as well.

Signed-off-by: Haim Dreyfuss <haim.dreyfuss@intel.com>
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>