Bump scaling to 1000.

Note the error in integer arithmetic

include/ucore/rate_limit.h

@@ -34,6 +34,13 @@
  *
  * uc_ratelimit_init(&r,20, 1, time(NULL));
  *
+ * NOTE. The the internals uses integer arithmetic to replenish the tickets,
+ * this can lead to greater errors estimating the available tickets the smaller
+ * the number of tickets is in relation to the period. The arithmetic is scaled
+ * by 1000 currently, so if ticket = 1 and period = 60, we get 1000/60 = 16. This
+ * should be 16.6667, which is an error of about 3.6%, which means we really just
+ * rate limit to 1 per 62 seconds.
+ *
  * for (;;) {
  *    int fd = accept(..);
  *    if (uc_ratelimit_allow(&r, time(NULL)) {

src/rate_limit.c

@@ -1,6 +1,6 @@
 #include "ucore/rate_limit.h"
 
-#define SCALE_FACTOR 100
+#define SCALE_FACTOR 1000
 
 
 void uc_ratelimit_init(struct RateLimit *r, long tickets, long period, long current_ts)