iwlwifi: show current tx power

debugFs file show current tx power for all the transmit chains

Adding "tx_power" file in /sys/kernal/debug/ieee80211/phy0/iwlagn/debug
to display current tx power for all the active chains in 1/2 dB step.

Show tx power information "Not available" if uCode can not provide the
information or interface is down.

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>
diff --git a/drivers/net/wireless/iwlwifi/iwl-debug.h b/drivers/net/wireless/iwlwifi/iwl-debug.h
index 723f38a..cbc6290 100644
--- a/drivers/net/wireless/iwlwifi/iwl-debug.h
+++ b/drivers/net/wireless/iwlwifi/iwl-debug.h
@@ -107,6 +107,7 @@
 		struct dentry *file_ucode_general_stats;
 		struct dentry *file_sensitivity;
 		struct dentry *file_chain_noise;
+		struct dentry *file_tx_power;
 	} dbgfs_debug_files;
 	u32 sram_offset;
 	u32 sram_len;