nfp: inform the VF driver needs to be restarted after changing the MAC

Add message to inform the VF MAC was changed and the need to restart
the VF driver for the changes to be effective.

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