timemaster: Wait for udev to set up vclock devices.

timemaster created vclock /dev/ptp devices (by writing to
/sys/class/ptp/ptp?/n_vclocks) and immediately started ptp4l
instances using those vclocks. It's a race condition. On a
SELinux-enabled system ptp4l was observed to exit with an error due to
the device not having its SELinux context set by udev yet.

Add a 100-millisecond sleep after creating the vclocks to give udev time
to finish its job before starting ptp4l instances.

Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>

timemaster.c

@@ -1240,12 +1240,18 @@ static int create_vclocks(struct phc_vclocks **phc_vclocks)
 {
 	struct phc_vclocks **vclocks;
 
+	if (!*phc_vclocks)
+		return 0;
+
 	for (vclocks = phc_vclocks; *vclocks; vclocks++) {
 		if (set_phc_n_vclocks((*vclocks)->pclock_index,
 				      (*vclocks)->vclocks))
 			return 1;
 	}
 
+	/* Wait for udev to set up the new /dev/ptp* devices */
+	usleep(100000);
+
 	return 0;
 }