nfp: add ndo_set_mac_address for representors

Adding a netdev to a bond requires that its mac address can be modified.
The default eth_mac_addr is sufficient to satisfy this requirement.

Signed-off-by: John Hurley <john.hurley@netronome.com>
Reviewed-by: Pieter Jansen van Vuuren <pieter.jansenvanvuuren@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>