enetc: add software timestamping

Provide a software TX timestamp and add it to the ethtool query
interface.

skb_tx_timestamp() is also needed if one would like to use PHY
timestamping.

Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: David S. Miller <davem@davemloft.net>
2 files changed