mavlink: add class for command retransmission

This adds a class to allow for retransmission of outgoing commands.
The sent commands are kept in a timestamped list to check if they are
acked as required by the mavlink protocol.
If they are not acked within a timeout, they can be retransmitted.

src/modules/mavlink/mavlink_receiver.cpp

@@ -88,6 +88,7 @@
 #include "mavlink_bridge_header.h"
 #include "mavlink_receiver.h"
 #include "mavlink_main.h"
+#include "mavlink_command_sender.h"
 
 static const float mg2ms2 = CONSTANTS_ONE_G / 1000.0f;
 
@@ -628,6 +629,8 @@ MavlinkReceiver::handle_message_command_ack(mavlink_message_t *msg)
 	mavlink_msg_command_ack_decode(msg, &ack);
 
 	if (ack.result != MAV_RESULT_ACCEPTED && ack.result != MAV_RESULT_IN_PROGRESS) {
+		MavlinkCommandSender::instance().handle_mavlink_command_ack(ack, msg->sysid, msg->compid);
+
 		if (msg->compid == MAV_COMP_ID_CAMERA) {
 			PX4_WARN("Got unsuccessful result %d from camera", ack.result);
 		}