Add macb_change_mtu callback; if jumbo frame support is present allow
mtu size changes upto (jumbo max length allowed - headers).
Signed-off-by: Harini Katakam <harinik@xilinx.com>
Reviewed-by: Punnaiah Choudary Kalluri <punnaia@xilinx.com>
Signed-off-by: David S. Miller <davem@davemloft.net>