iwlwifi: mvm: support queue removal in ADD_STA hcmd

To indicate to the FW that a queue has been removed, an
existing flag in the ADD_STA HCMD (that hasn't been in use)
has been changed to indicate that a queue is being removed
from a STA.

Update this in the driver code.

Signed-off-by: Liad Kaufman <liad.kaufman@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>