mac80211: fix warning on htmldocs for last_tdls_pkt_time

Forgot to add an entry to the struct description of sta_info.
Signed-off-by: Liad Kaufman <liad.kaufman@intel.com>
Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/sta_info.h

@@ -336,6 +336,7 @@ struct ieee80211_tx_latency_stat {
  * @known_smps_mode: the smps_mode the client thinks we are in. Relevant for
  *	AP only.
  * @cipher_scheme: optional cipher scheme for this station
+ * @last_tdls_pkt_time: holds the time in jiffies of last TDLS pkt ACKed
  */
 struct sta_info {
 	/* General information, mostly static */