net/macb: manage carrier state with call to netif_carrier_{on|off}()

OFF carrier state is setup in probe() open() and suspend() functions.
The carrier ON state is managed in macb_handle_link_change().

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>