iwlwifi: add rf information in rate_scale debugfs command

Adding more Radio information when displaying
rate_scale_table. This can help to understand how many antenna and the
current RF condition such as SISO, MIMO2, MIMO3.

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>