X host: ↑nhit a bit

to get more details in latency distribution

ioping.c

@@ -1072,7 +1072,7 @@ static void random_memory(void *buf, size_t len)
 	}
 }
 
-#define HIST_NHIT 10
+#define HIST_NHIT 20
 struct statistics {
 	long long start, finish, load_time;
 	long long count, valid, too_slow, too_fast;