iwlwifi: bit field description for BT Config command

Give better bit filed define and description for flag parameter
in REPLY_BT_CONFIG command:

flags:
 bit 0 - 1: BT channel announcement enabled
         0: disable
 bit 1 - 1: priority of BT device enabled
         0: disable
 bit 2 - 1: BT 2 wire support enabled
         0: disable

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>