net: Make net_hwtstamp_validate accessible

Make the net_hwtstamp_validate function accessible in prevision to use
it from ethtool to validate the hwtstamp configuration before setting it.

Reviewed-by: Florian Fainelli <[e-mail]>
Reviewed-by: Jacob Keller <[e-mail]>
Signed-off-by: Kory Maincent <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/core/dev.h

···
 			    struct netlink_ext_ack *extack);
 int dev_get_hwtstamp_phylib(struct net_device *dev,
 			    struct kernel_hwtstamp_config *cfg);
+int net_hwtstamp_validate(const struct kernel_hwtstamp_config *cfg);
 
 #endif

net/core/dev_ioctl.c

···
 	return err;
 }
 
-static int net_hwtstamp_validate(const struct kernel_hwtstamp_config *cfg)
+int net_hwtstamp_validate(const struct kernel_hwtstamp_config *cfg)
 {
 	enum hwtstamp_tx_types tx_type;
 	enum hwtstamp_rx_filters rx_filter;