net: lan966x: Fix 1-step timestamping over ipv4 or ipv6

net: lan966x: Fix 1-step timestamping over ipv4 or ipv6

When enabling 1-step timestamping for ptp frames that are over udpv4 or
udpv6 then the inserted timestamp is added at the wrong offset in the
frame, meaning that will modify the frame at the wrong place, so the
frame will be malformed.
To fix this, the HW needs to know which kind of frame it is to know
where to insert the timestamp. For that there is a field in the IFH that
says the PDU_TYPE, which can be NONE  which is the default value,
IPV4 or IPV6. Therefore make sure to set the PDU_TYPE so the HW knows
where to insert the timestamp.
Like I mention before the issue is not seen with L2 frames because by
default the PDU_TYPE has a value of 0, which represents the L2 frames.

Fixes: 77eecf25bd9d2f ("net: lan966x: Update extraction/injection for timestamping")
Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Link: https://patch.msgid.link/20250521124159.2713525-1-horatiu.vultur@microchip.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>