net: enetc: move sync packet modification before dma_map_single()

net: enetc: move sync packet modification before dma_map_single()

Move sync packet content modification before dma_map_single() to follow
correct DMA usage process, even though the previous sequence worked due
to hardware DMA-coherence support (LS1028A). But for the upcoming i.MX95,
its ENETC (v4) does not support "dma-coherent", so this step is very
necessary. Otherwise, the originTimestamp and correction fields of the
sent packets will still be the values before the modification.

Signed-off-by: Wei Fang <wei.fang@nxp.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20250829050615.1247468-13-wei.fang@nxp.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>