i40e: defeature support for PTP L4 frame detection on XL710

A product decision has been made to defeature detection of PTP frames
over L4 (UDP) on the XL710 MAC. Do not advertise support for L4
timestamping.

Change-ID: I41fbb0f84ebb27c43e23098c08156f2625c6ee06
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>