bridge: implement multicast fast leave

V2: make the toggle per-port

Fast leave allows bridge to immediately stops the multicast
traffic on the port receives IGMP Leave when IGMP snooping is enabled,
no timeouts are observed.

Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Stephen Hemminger <shemminger@vyatta.com>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Cong Wang <amwang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index 2417434..2391bae 100644
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -1225,6 +1225,27 @@
 	if (!mp)
 		goto out;
 
+	if (port && port->multicast_fast_leave) {
+		struct net_bridge_port_group __rcu **pp;
+
+		for (pp = &mp->ports;
+		     (p = mlock_dereference(*pp, br)) != NULL;
+		     pp = &p->next) {
+			if (p->port != port)
+				continue;
+
+			rcu_assign_pointer(*pp, p->next);
+			hlist_del_init(&p->mglist);
+			del_timer(&p->timer);
+			call_rcu_bh(&p->rcu, br_multicast_free_pg);
+
+			if (!mp->ports && !mp->mglist &&
+			    netif_running(br->dev))
+				mod_timer(&mp->timer, jiffies);
+		}
+		goto out;
+	}
+
 	now = jiffies;
 	time = now + br->multicast_last_member_count *
 		     br->multicast_last_member_interval;