net: ethtool: fix spelling mistake: "tubale" -> "tunable"

Signed-off-by: Michael Heimpold <mhei@heimpold.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/ethtool.h

@@ -226,7 +226,7 @@ enum tunable_id {
 	ETHTOOL_TX_COPYBREAK,
 	ETHTOOL_PFC_PREVENTION_TOUT, /* timeout in msecs */
 	/*
-	 * Add your fresh new tubale attribute above and remember to update
+	 * Add your fresh new tunable attribute above and remember to update
 	 * tunable_strings[] in net/core/ethtool.c
 	 */
 	__ETHTOOL_TUNABLE_COUNT,