Broken condition in check_expired_networkstatus_callback()

Turns out that this condition in check_expired_networkstatus_callback():

  if (ns && ns->valid_until < now+NS_EXPIRY_SLOP &&
      router_have_minimum_dir_info()) {
    router_dir_info_changed();
  }

... is always true if we have all our needed directory info which means that router_dir_info_changed() is called every 2 minutes (the callback interval).

Nick suggested that it should be now - NS_EXPIRY_SLOP which goes like this:

If valid_until is 6am today, then now - 24h == 1pm yesterday, and valid_until < (now - 24h) is false. But at 6:01am tomorrow, valid_until < now - 24h becomes true.