iwlwifi: disable FAT channel when not permitted

This patch disables FAT channel when it is not permitted according to
the EEPROM.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>