bridge: use rx_handler_data pointer to store net_bridge_port pointer

Register net_bridge_port pointer as rx_handler data pointer. As br_port is
removed from struct net_device, another netdev priv_flag is added to indicate
the device serves as a bridge port. Also rcuized pointers are now correctly
dereferenced in br_fdb.c and in netfilter parts.

Signed-off-by: Jiri Pirko <jpirko@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>