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_sysfs_if.c b/net/bridge/br_sysfs_if.c
index 7ff95ba..dc484ac 100644
--- a/net/bridge/br_sysfs_if.c
+++ b/net/bridge/br_sysfs_if.c
@@ -172,6 +172,25 @@
 }
 static BRPORT_ATTR(multicast_router, S_IRUGO | S_IWUSR, show_multicast_router,
 		   store_multicast_router);
+
+static ssize_t show_multicast_fast_leave(struct net_bridge_port *p,
+					 char *buf)
+{
+	return sprintf(buf, "%d\n", p->multicast_fast_leave);
+}
+
+static int store_multicast_fast_leave(struct net_bridge_port *p,
+				      unsigned long v)
+{
+	if (p->br->multicast_disabled)
+		return -EINVAL;
+
+	p->multicast_fast_leave = !!v;
+	return 0;
+}
+
+static BRPORT_ATTR(multicast_fast_leave, S_IRUGO | S_IWUSR,
+		   show_multicast_fast_leave, store_multicast_fast_leave);
 #endif
 
 static const struct brport_attribute *brport_attrs[] = {
@@ -195,6 +214,7 @@
 	&brport_attr_root_block,
 #ifdef CONFIG_BRIDGE_IGMP_SNOOPING
 	&brport_attr_multicast_router,
+	&brport_attr_multicast_fast_leave,
 #endif
 	NULL
 };