iwlwifi: mvm: Insert DS Parameter Set placeholder in probes

Since it's too complicated for the fw to insert a DS Parameter Set
element in the middle of the frame, it was decided that it should be
done by the host. The fw will only parse the frame and update the
current channel field.

Signed-off-by: Andrei Otcheretianski <andrei.otcheretianski@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>