net: ethtool: ts: Update GET_TS to reply the current selected timestamp

As the default selected timestamp API change we have to change also the
timestamp return by ethtool. This patch return now the current selected
timestamp.

Signed-off-by: Kory Maincent <kory.maincent@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>