iwlwifi: mvm: don't override passive dwell in case of fragmented scan

Currently scan params structure has only active or passive dwell time
fields, passive one is used for fragmented scans too. FW needs the
passive dwell time even when performing fragmented scan for calculating
time between channels. Add a separate parameter for fragmented dwell time
and pass both fragmented and passive to FW.

Signed-off-by: David Spinadel <david.spinadel@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>