nl80211: Optimize cfg80211_bss_expire invocations

Only invoke cfg80211_bss_expire on the first nl80211_dump_scan
invocation to avoid (likely) redundant processing.
Signed-off-by: Denis Kenzior <denkenz@gmail.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/wireless/nl80211.c

@@ -8100,7 +8100,15 @@ static int nl80211_dump_scan(struct sk_buff *skb, struct netlink_callback *cb)
 
 	wdev_lock(wdev);
 	spin_lock_bh(&rdev->bss_lock);
-	cfg80211_bss_expire(rdev);
+
+	/*
+	 * dump_scan will be called multiple times to break up the scan results
+	 * into multiple messages.  It is unlikely that any more bss-es will be
+	 * expired after the first call, so only call only call this on the
+	 * first dump_scan invocation.
+	 */
+	if (start == 0)
+		cfg80211_bss_expire(rdev);
 
 	cb->seq = rdev->bss_generation;