iwlwifi: pcie: stop sending commands to dead firmware

If we call ieee80211_hw_restart, it means that the
firmware is in bad condition and will be reset soon.
Since the firmware will be reset, there is no good
reason to keep sending host commands.

Signed-off-by: Alexander Bondar <alexander.bondar@intel.com>
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>