mac80211: add missing kernel-doc

Document the new shutdown member.
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/sta_info.h

@@ -90,6 +90,7 @@ struct tid_ampdu_tx {
  * @buf_size: buffer size for incoming A-MPDUs
  * @timeout: reset timer value (in TUs).
  * @dialog_token: dialog token for aggregation session
+ * @shutdown: this session is being shut down due to STA removal
  */
 struct tid_ampdu_rx {
 	struct sk_buff **reorder_buf;