If vlan has been enabled. ifdown followed by ifup will lost hardware
related state.

Also remove duplicated operation in gfar_vlan_rx_register().
Signed-off-by: NYong Zhang <yong.zhang0@gmail.com>
Acked-by: NDai Haruki <dai.haruki@freescale.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>