mac80211: Fix documentation strings for airtime-related variables

There was a typo in the documentation for weight_multiplier in mac80211.h,
and the doc was missing entirely for airtime and airtime_weight in sta_info.h.

Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/sta_info.h

@@ -473,6 +473,9 @@ struct ieee80211_sta_rx_stats {
  * @last_seq_ctrl: last received seq/frag number from this STA (per TID
  *	plus one for non-QoS frames)
  * @tid_seq: per-TID sequence numbers for sending to this STA
+ * @airtime: per-AC struct airtime_info describing airtime statistics for this
+ *	station
+ * @airtime_weight: station weight for airtime fairness calculation purposes
  * @ampdu_mlme: A-MPDU state machine state
  * @mesh: mesh STA information
  * @debugfs_dir: debug filesystem directory dentry