ipv4: fib_rules: Fix possible infinite loop in fib_empty_table

gcc warn this:
net/ipv4/fib_rules.c:203 fib_empty_table() warn:
 always true condition '(id <= 4294967295) => (0-u32max <= u32max)'

'id' is u32, which always not greater than RT_TABLE_MAX
(0xFFFFFFFF), So add a check to break while wrap around.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/fib_rules.c

@@ -198,11 +198,15 @@ static int fib4_rule_match(struct fib_rule *rule, struct flowi *fl, int flags)
 
 static struct fib_table *fib_empty_table(struct net *net)
 {
-	u32 id;
+	u32 id = 1;
 
-	for (id = 1; id <= RT_TABLE_MAX; id++)
+	while (1) {
 		if (!fib_get_table(net, id))
 			return fib_new_table(net, id);
+
+		if (id++ == RT_TABLE_MAX)
+			break;
+	}
 	return NULL;
 }