pch_gbe: run the ptp bpf just once per packet

This patch fixes code which needlessly ran the BPF twice per
packet. Instead, we just run the classifier once and test
whether the packet is any kind of PTP event message.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>