static int receivers_sort(void *_a, void *_b) {
  struct receiver *a = (struct receiver *)_a;
  struct receiver *b = (struct receiver *)_b;

  return(b->num_pkts - a->num_pkts);
}
static int receivers_sort(void *_a, void *_b) {
  struct receiver *a = (struct receiver *)_a;
  struct receiver *b = (struct receiver *)_b;

  return(b->num_pkts - a->num_pkts);
}