x86: Work around compiler code generation bug with -Os

Some versions of gcc generate incorrect code for the inet_check_attr()
function, apparently due to a totally bogus index -> pointer comparison
transformation.

At least "gcc version 4.0.1 20050727 (Red Hat 4.0.1-5)" from FC4 is
affected, possibly others too.

This changes the function subtly so that the buggy gcc transformation
doesn't trigger.
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

net/ipv4/fib_frontend.c

@@ -289,13 +289,13 @@ static int inet_check_attr(struct rtmsg *r, struct rtattr **rta)
 {
 	int i;
 
-	for (i=1; i<=RTA_MAX; i++) {
-		struct rtattr *attr = rta[i-1];
+	for (i=1; i<=RTA_MAX; i++, rta++) {
+		struct rtattr *attr = *rta;
 		if (attr) {
 			if (RTA_PAYLOAD(attr) < 4)
 				return -EINVAL;
 			if (i != RTA_MULTIPATH && i != RTA_METRICS)
-				rta[i-1] = (struct rtattr*)RTA_DATA(attr);
+				*rta = (struct rtattr*)RTA_DATA(attr);
 		}
 	}
 	return 0;