iwlwifi: mvm: configure wowlan configuration only if connected

Recent fw version added assert to make sure wowlan configuration
is configured only when a station is connected.

Change the driver behavior to pass this configuration only
if we indeed have ap station id (i.e. connected).

Signed-off-by: Eliad Peller <eliadx.peller@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>