iwlwifi: return commands with error on FW error

When a firmware error occurs, don't just abort synchronous
commands but also return an error (-EIO) and block any new
commands as well. Currently, an error is only returned if
WANT_SKB was set which is confusing and can lead to issues.

Blocking is done until a new firmware image is loaded.

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