mavlink_receiver: process MAV_CMD_WAYPOINT_USER_1 as a command to process a custom action

The custom action is to be processed by an entity external to the FMU.

src/modules/mavlink/mavlink_receiver.cpp

@@ -680,6 +680,29 @@ void MavlinkReceiver::handle_message_command_both(mavlink_message_t *msg, const
 				break;
 			}
 
+		} else if (cmd_mavlink.command == MAV_CMD_WAYPOINT_USER_1) {
+			// Processes MAV_CMD_WAYPOINT_USER_1 as a custom action command to be
+			// processed by a mission computer. For more context, check the MAVSDK
+			// PR in this link: https://github.com/mavlink/MAVSDK/pull/1581
+			//
+			// Note: this command will be eventually replaced by the command proposed
+			// in https://github.com/mavlink/mavlink/pull/1516 or similar
+			//
+			// Note for this case, the command is sent from an external entity
+			// to trigger a custom action on the Mission Computer, so a timeout
+			// check is not handled by the autopilot, but should rather be handled
+			// by the entity sending this command
+			vehicle_command_s custom_action_cmd = vehicle_command;
+			custom_action_cmd.target_system = 0;
+			custom_action_cmd.target_component = 0; // Broadcast the command
+			custom_action_cmd.from_external = false;
+
+			PX4_DEBUG("received MAV_CMD_WAYPOINT_USER_1 command from %d/%d", custom_action_cmd.command,
+				  custom_action_cmd.source_system,
+				  custom_action_cmd.source_component);
+
+			_cmd_pub.publish(custom_action_cmd);
+
 		} else {
 			result = vehicle_command_ack_s::VEHICLE_RESULT_UNSUPPORTED;
 		}