Set timestamp with vehicle commands

The vehicle_command uORB messages had the timestamp unset at 0.

src/modules/commander/commander.cpp

@@ -495,6 +495,8 @@ int commander_main(int argc, char *argv[])
 				cmd.param6 = NAN;
 				cmd.param7 = NAN;
 
+				cmd.timestamp = hrt_absolute_time();
+
 				orb_advert_t h = orb_advertise_queue(ORB_ID(vehicle_command), &cmd, vehicle_command_s::ORB_QUEUE_LENGTH);
 				(void)orb_unadvertise(h);