net: ptp: fix time stamp matching logic for VLAN packets.

Commit ae5c6c6d "ptp: Classify ptp over ip over vlan packets" changed the
code in two drivers that matches time stamps with PTP frames, with the goal
of allowing VLAN tagged PTP packets to receive hardware time stamps.

However, that commit failed to account for the VLAN header when parsing
IPv4 packets. This patch fixes those two drivers to correctly match VLAN
tagged IPv4/UDP PTP messages with their time stamps.

This patch should also be applied to v3.17.

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