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: NPablo Cascón <pablo.cascon@netronome.com>
Reviewed-by: NJakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>