phy: warn if phylib and ethtool PHY mode definitions are out of sync

If new PHY modes are added people may miss to update all relevant places
in the kernel. Therefore add a build bug check for new modes in enum
ethtool_link_mode_bit_indices that haven't been added to phylib yet.

Suggested-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/phy-core.c

@@ -8,6 +8,11 @@
 
 const char *phy_speed_to_str(int speed)
 {
+	BUILD_BUG_ON_MSG(__ETHTOOL_LINK_MODE_MASK_NBITS != 67,
+		"Enum ethtool_link_mode_bit_indices and phylib are out of sync. "
+		"If a speed or mode has been added please update phy_speed_to_str "
+		"and the PHY settings array.\n");
+
 	switch (speed) {
 	case SPEED_10:
 		return "10Mbps";