ixgbe: Reset max_vfs to zero when user request is out of range

If the user request for the number of VFs in the max_vfs parameter is
out of range then reset the value to the default value of zero.  This
makes the behavior of the ixgbe driver the same as for the igb driver.

Signed-off-by: Greg Rose <gregory.v.rose@intel.com>
Tested-by: Robert Garrett <robertx.e.garrett@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>