bridge: implement multicast fast leave V3: make it a flag 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 <[email protected]> Cc: Stephen Hemminger <[email protected]> Cc: "David S. Miller" <[email protected]> Signed-off-by: Cong Wang <[email protected]>