Set timestamp with vehicle commands

The vehicle_command uORB messages had the timestamp unset at 0.

src/drivers/camera_trigger/camera_trigger.cpp

@@ -484,6 +484,7 @@ void
 CameraTrigger::test()
 {
 	struct vehicle_command_s cmd = {};
+	cmd.timestamp = hrt_absolute_time();
 	cmd.command = vehicle_command_s::VEHICLE_CMD_DO_DIGICAM_CONTROL;
 	cmd.param5 = 1.0f;