net: enetc: don't update sync packet checksum if checksum offload is used

For ENETC v4, the hardware has the capability to support Tx checksum
offload. so the enetc driver does not need to update the UDP checksum
of PTP sync packets if Tx checksum offload is enabled.

Signed-off-by: Wei Fang <wei.fang@nxp.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20250829050615.1247468-15-wei.fang@nxp.com


Signed-off-by: Paolo Abeni <pabeni@redhat.com>