net: loopback: use generic helper to report timestamping info

For reporting the common set of SW timestamping capabilities, use
ethtool_op_get_ts_info() instead of re-implementing it.
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/loopback.c

@@ -128,21 +128,9 @@ static u32 always_on(struct net_device *dev)
 	return 1;
 }
 
-static int loopback_get_ts_info(struct net_device *netdev,
-				struct ethtool_ts_info *ts_info)
-{
-	ts_info->so_timestamping = SOF_TIMESTAMPING_TX_SOFTWARE |
-				   SOF_TIMESTAMPING_RX_SOFTWARE |
-				   SOF_TIMESTAMPING_SOFTWARE;
-
-	ts_info->phc_index = -1;
-
-	return 0;
-};
-
 static const struct ethtool_ops loopback_ethtool_ops = {
 	.get_link		= always_on,
-	.get_ts_info		= loopback_get_ts_info,
+	.get_ts_info		= ethtool_op_get_ts_info,
 };
 
 static int loopback_dev_init(struct net_device *dev)