nl80211: allow BSS data to include CLOCK_BOOTTIME timestamp

For location and connectivity services, userspace would often like
to know the time when the BSS was last seen. The current "last seen"
value is calculated in a way that makes it less useful, especially
if the system suspended in the meantime.

Add the ability for the driver to report a real CLOCK_BOOTTIME stamp
that can then be reported to userspace (if present).

Drivers wishing to use this must be converted to the new API to call
cfg80211_inform_bss_data() or cfg80211_inform_bss_frame_data(). They
need to ensure the reported value is accurate enough even when the
frame might have been buffered in the device (e.g. firmware.)

Signed-off-by: Dmitry Shmidt <dimitrysh@google.com>
[modified to use struct, inlines]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/uapi/linux/nl80211.h

@@ -3364,6 +3364,9 @@ enum nl80211_bss_scan_width {
  *	(not present if no beacon frame has been received yet)
  * @NL80211_BSS_PRESP_DATA: the data in @NL80211_BSS_INFORMATION_ELEMENTS and
  *	@NL80211_BSS_TSF is known to be from a probe response (flag attribute)
+ * @NL80211_BSS_LAST_SEEN_BOOTTIME: CLOCK_BOOTTIME timestamp when this entry
+ *	was last updated by a received frame. The value is expected to be
+ *	accurate to about 10ms. (u64, nanoseconds)
  * @__NL80211_BSS_AFTER_LAST: internal
  * @NL80211_BSS_MAX: highest BSS attribute
  */
@@ -3383,6 +3386,7 @@ enum nl80211_bss {
 	NL80211_BSS_CHAN_WIDTH,
 	NL80211_BSS_BEACON_TSF,
 	NL80211_BSS_PRESP_DATA,
+	NL80211_BSS_LAST_SEEN_BOOTTIME,
 
 	/* keep last */
 	__NL80211_BSS_AFTER_LAST,