bridge: move to workqueue gc

Move the fdb garbage collector to a workqueue which fires at least 10
milliseconds apart and cleans chain by chain allowing for other tasks
to run in the meantime. When having thousands of fdbs the system is much
more responsive. Most importantly remove the need to check if the
matched entry has expired in __br_fdb_get that causes false-sharing and
is completely unnecessary if we cleanup entries, at worst we'll get 10ms
of traffic for that entry before it gets deleted.

Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/bridge/br_ioctl.c b/net/bridge/br_ioctl.c
index da8157c..7970f85 100644
--- a/net/bridge/br_ioctl.c
+++ b/net/bridge/br_ioctl.c
@@ -149,7 +149,7 @@ static int old_dev_ioctl(struct net_device *dev, struct ifreq *rq, int cmd)
 		b.hello_timer_value = br_timer_value(&br->hello_timer);
 		b.tcn_timer_value = br_timer_value(&br->tcn_timer);
 		b.topology_change_timer_value = br_timer_value(&br->topology_change_timer);
-		b.gc_timer_value = br_timer_value(&br->gc_timer);
+		b.gc_timer_value = br_timer_value(&br->gc_work.timer);
 		rcu_read_unlock();
 
 		if (copy_to_user((void __user *)args[1], &b, sizeof(b)))