Release all resources when quitting the main loop.

This will allow running under valgrind to detect memory leaks
and the like.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>

ptp4l.c

@@ -279,5 +279,6 @@ int main(int argc, char *argv[])
 			break;
 	}
 
+	clock_destroy(clock);
 	return 0;
 }