iwlwifi: fix FW restart on init FW

When unregistered with mac80211, we can't call its functionality
for FW restart, so avoid it and prevent automatic FW restart for
the init firmware.

Signed-off-by: Amit Beka <amit.beka@intel.com>
Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>