ethtool: Move n-tuple capability check into set_flags

set_flags should check if the underlying device supports
n-tuple filter programming before setting the device flags
on the netdevice.

Signed-off-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>