[NET]: Corrects a bug in ip_rt_acct_read()

It seems that stats of cpu 0 are counted twice, since
for_each_possible_cpu() is looping on all possible cpus, including 0

Before percpu conversion of ip_rt_acct, we should also remove the
assumption that CPU 0 is online (or even possible)
Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/route.c

@@ -2888,18 +2888,14 @@ static int ip_rt_acct_read(char *buffer, char **start, off_t offset,
 	offset /= sizeof(u32);
 
 	if (length > 0) {
-		u32 *src = ((u32 *) IP_RT_ACCT_CPU(0)) + offset;
 		u32 *dst = (u32 *) buffer;
 
-		/* Copy first cpu. */
 		*start = buffer;
-		memcpy(dst, src, length);
+		memset(dst, 0, length);
 
-		/* Add the other cpus in, one int at a time */
 		for_each_possible_cpu(i) {
 			unsigned int j;
-
-			src = ((u32 *) IP_RT_ACCT_CPU(i)) + offset;
+			u32 *src = ((u32 *) IP_RT_ACCT_CPU(i)) + offset;
 
 			for (j = 0; j < length/4; j++)
 				dst[j] += src[j];