i40e: re-enable PTP L4 capabilities for XL710 if FW >6.0

Starting with XL710 FW 5.3 PTP L4 was disabled for XL710 due to a bug.  The
bug has since been resolved in XL710 FW >6.0 and PTP L4 can now be
re-enabled on those devices with updated firmware.

Signed-off-by: Alan Brady <alan.brady@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>