igb: enable l4 timestamping for v2 event packets

When enabling hardware timestamping for ptp v2 event packets, the
software does not setup the queue for l4 packets, although layer 4
packets are valid for v2. This patch adds the flag which enables
setting up a queue and enabling udp packet timestamping.

Signed-off-by: Jacob E Keller <jacob.e.keller@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>