iwlwifi: disable AP mode

iwlwifi does not support AP mode in any way. For one, it doesn't even
buffer multicast/broadcast frames properly. We didn't allow zd1211rw AP
mode to be enabled without this, so iwlwifi shouldn't be allowed to
advertise AP mode either.

It also doesn't work at all, it doesn't even answer to probe requests,
I'm guessing the packet injection code was disabled again.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Acked-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>