mac80211: rename bss_conf timestamp to last_tsf

This value is not really very useful by itself,
yet some drivers (including iwlwifi until I can
figure out what it should do) use it. At least
rename it to "last_tsf" to indicate the meaning
and add a note that it may be really old.

I suspect the value may become useful combined
with the rx_status->mactime, but we don't (yet)
store that value and pass it to the driver.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/net/mac80211/mlme.c b/net/mac80211/mlme.c
index 39c1393..90d1db3 100644
--- a/net/mac80211/mlme.c
+++ b/net/mac80211/mlme.c
@@ -1318,7 +1318,7 @@
 	bss_info_changed |= BSS_CHANGED_ASSOC;
 	/* set timing information */
 	bss_conf->beacon_int = cbss->beacon_interval;
-	bss_conf->timestamp = cbss->tsf;
+	bss_conf->last_tsf = cbss->tsf;
 
 	bss_info_changed |= BSS_CHANGED_BEACON_INT;
 	bss_info_changed |= ieee80211_handle_bss_capability(sdata,