iwlwifi: mvm: update firmware of VHT MU-MIMO groups status on restart

The firmware handles the VHT MU-MIMO group data on its own.
However, on HW restart (and future sniffer mode) the driver
shall update the firmware on the VHT MU-MIMO group membership
status.

Signed-off-by: Sara Sharon <sara.sharon@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>