i40e: Use ethtool private flags to display NPAR status

Allow an application to query the i40e driver's private flags to get the
status of NPAR enablement.  This will be used by applications to determine
if there are NPAR specific features available.

Change-ID: Ia6d9477a48f9c4cb41ca022bd433f77da3f2146c
Signed-off-by: Greg Rose <gregory.v.rose@intel.com>
Tested-by: Jim Young <james.m.young@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>