ethtool: provide timestamping information with TSINFO_GET request

Implement TSINFO_GET request to get timestamping information for a network
device. This is traditionally available via ETHTOOL_GET_TS_INFO ioctl
request.

Move part of ethtool_get_ts_info() into common.c so that ioctl and netlink
code use the same logic to get timestamping information from the device.

v3: use "TSINFO" rather than "TIMESTAMP", suggested by Richard Cochran

Signed-off-by: Michal Kubecek <mkubecek@suse.cz>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ethtool/common.h b/net/ethtool/common.h
index c54c8d5..a62f68cc 100644
--- a/net/ethtool/common.h
+++ b/net/ethtool/common.h
@@ -35,5 +35,6 @@ bool convert_legacy_settings_to_link_ksettings(
 	struct ethtool_link_ksettings *link_ksettings,
 	const struct ethtool_cmd *legacy_settings);
 int ethtool_get_max_rxfh_channel(struct net_device *dev, u32 *max);
+int __ethtool_get_ts_info(struct net_device *dev, struct ethtool_ts_info *info);
 
 #endif /* _ETHTOOL_COMMON_H */