rt_cpu_seq_next should increase position index

if seq_file .next fuction does not change position index,
read after some lseek can generate unexpected output.

https://bugzilla.kernel.org/show_bug.cgi?id=206283
Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/route.c

@@ -271,6 +271,7 @@ static void *rt_cpu_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 		*pos = cpu+1;
 		return &per_cpu(rt_cache_stat, cpu);
 	}
+	(*pos)++;
 	return NULL;
 
 }