net: ethtool: Fix comment mentioning typo in IS_ENABLED()

This has no code changes, but it's a typo noticed in other clean-ups,
so we might as well fix it. IS_ENABLED() takes full names, and should
have the "CONFIG_" prefix.
Reported-by: Joe Perches <joe@perches.com>
Link: https://lore.kernel.org/lkml/b08611018fdb6d88757c6008a5c02fa0e07b32fb.camel@perches.comSigned-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/ethtool_netlink.h

@@ -67,5 +67,5 @@ static inline int ethnl_cable_test_step(struct phy_device *phydev, u32 first,
 {
 	return -EOPNOTSUPP;
 }
-#endif /* IS_ENABLED(ETHTOOL_NETLINK) */
+#endif /* IS_ENABLED(CONFIG_ETHTOOL_NETLINK) */
 #endif /* _LINUX_ETHTOOL_NETLINK_H_ */