cfg80211: Support assoc-at timer in sta-info

Report timestamp of when sta became associated.

This is the boottime clock, units are nano-seconds.
Signed-off-by: Ben Greear <greearb@candelatech.com>
Link: https://lore.kernel.org/r/20190809180001.26393-1-greearb@candelatech.comSigned-off-by: Johannes Berg <johannes.berg@intel.com>

include/net/cfg80211.h

@@ -1330,6 +1330,7 @@ struct cfg80211_tid_stats {
  *	indicate the relevant values in this struct for them
  * @connected_time: time(in secs) since a station is last connected
  * @inactive_time: time since last station activity (tx/rx) in milliseconds
+ * @assoc_at: bootime (ns) of the last association
  * @rx_bytes: bytes (size of MPDUs) received from this station
  * @tx_bytes: bytes (size of MPDUs) transmitted to this station
  * @llid: mesh local link id
@@ -1390,6 +1391,7 @@ struct station_info {
 	u64 filled;
 	u32 connected_time;
 	u32 inactive_time;
+	u64 assoc_at;
 	u64 rx_bytes;
 	u64 tx_bytes;
 	u16 llid;

include/uapi/linux/nl80211.h

@@ -3201,6 +3201,8 @@ enum nl80211_sta_bss_param {
  *	sent to the station (u64, usec)
  * @NL80211_STA_INFO_AIRTIME_WEIGHT: current airtime weight for station (u16)
  * @NL80211_STA_INFO_AIRTIME_LINK_METRIC: airtime link metric for mesh station
+ * @NL80211_STA_INFO_ASSOC_AT_BOOTTIME: Timestamp (CLOCK_BOOTTIME, nanoseconds)
+ *	of STA's association
  * @__NL80211_STA_INFO_AFTER_LAST: internal
  * @NL80211_STA_INFO_MAX: highest possible station info attribute
  */
@@ -3247,6 +3249,7 @@ enum nl80211_sta_info {
 	NL80211_STA_INFO_TX_DURATION,
 	NL80211_STA_INFO_AIRTIME_WEIGHT,
 	NL80211_STA_INFO_AIRTIME_LINK_METRIC,
+	NL80211_STA_INFO_ASSOC_AT_BOOTTIME,
 
 	/* keep last */
 	__NL80211_STA_INFO_AFTER_LAST,

net/wireless/nl80211.c

@@ -5032,6 +5032,7 @@ static int nl80211_send_station(struct sk_buff *msg, u32 cmd, u32 portid,
 
 	PUT_SINFO(CONNECTED_TIME, connected_time, u32);
 	PUT_SINFO(INACTIVE_TIME, inactive_time, u32);
+	PUT_SINFO_U64(ASSOC_AT_BOOTTIME, assoc_at);
 
 	if (sinfo->filled & (BIT_ULL(NL80211_STA_INFO_RX_BYTES) |
 			     BIT_ULL(NL80211_STA_INFO_RX_BYTES64)) &&