bonding: use pre-defined macro in bond_mode_name instead of magic number 0

We have BOND_MODE_ROUNDROBIN pre-defined as 0, and it's the lowest
mode number.
Use it to check the arg lower bound instead of magic number 0 in
bond_mode_name.

Signed-off-by: Wang Sheng-Hui <shhuiw@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/bonding/bond_main.c

@@ -273,7 +273,7 @@ const char *bond_mode_name(int mode)
 		[BOND_MODE_ALB] = "adaptive load balancing",
 	};
 
-	if (mode < 0 || mode > BOND_MODE_ALB)
+	if (mode < BOND_MODE_ROUNDROBIN || mode > BOND_MODE_ALB)
 		return "unknown";
 
 	return names[mode];