ionic: support sr-iov operations

Add the netdev ops for managing VFs.  Since most of the
management work happens in the NIC firmware, the driver becomes
mostly a pass-through for the network stack commands that want
to control and configure the VFs.

We also tweak ionic_station_set() a little to allow for
the VFs that start off with a zero'd mac address.

Signed-off-by: Shannon Nelson <snelson@pensando.io>
Signed-off-by: David S. Miller <davem@davemloft.net>