ixgbe: fix the return value for unsupported VF offload

When failing the request because we can't support that offload,
reporting EOPNOTSUPP makes much more sense than ENXIO.

Signed-off-by: Shannon Nelson <shannon.nelson@oracle.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>