This will prevent from using unreliable frequency estimate on iburst
when starting without drift file.
The @code{maxupdateskew} parameter allows the threshold for determining
whether an estimate may be so unreliable that it should not be used.
+By default, the threshold is 1000 ppm.
The syntax is
static char *drift_file = NULL;
static char *rtc_file = NULL;
static unsigned long command_key_id;
-static double max_update_skew = DBL_MAX;
+static double max_update_skew = 1000.0;
static int cmd_port = -1;