iwlwifi: add missing comments

This patch add comments that escaped from the previous merge

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/iwlwifi/iwl-4965.h b/drivers/net/wireless/iwlwifi/iwl-4965.h
index 5a410e2..267ae75 100644
--- a/drivers/net/wireless/iwlwifi/iwl-4965.h
+++ b/drivers/net/wireless/iwlwifi/iwl-4965.h
@@ -516,7 +516,7 @@
 	u8 supported_chan_width;
 	u16 tx_mimo_ps_mode;
 	u8 is_green_field;
-	u8 sgf;
+	u8 sgf;			/* HT_SHORT_GI_* short guard interval */
 	u8 max_amsdu_size;
 	u8 ampdu_factor;
 	u8 mpdu_density;