iwlwifi: mvm: skip EBS in low latency mode while fragmented scan isn't supported

While associated in low latency mode, or when traffic load is high,
don't enable EBS in scan request if fragmented EBS is not supported
by the FW.

Signed-off-by: Ayala Beker <ayala.beker@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>