nfp: add set_mac_address support while the interface is up

Expose FW app ability to change MAC address at runtime.  Make sure
we only depend on it if FW app advertised the right capability.

Signed-off-by: Pablo Cascón <pablo.cascon@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>