team: remove duplicate set of flag IFF_MULTICAST

Remove unnecessary set of flag IFF_MULTICAST, since ether_setup
already does this.

Signed-off-by: Zhang Shengju <zhangshengju@cmss.chinamobile.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>