GCS_Common: whitelist AUTOPILOT_VERSION for in_delay_callback sending

GCSs may request this very early on in the boot process, particularly
for SITL.

If we try to send it during a delay callback then we end up dropping it
at the moment - but we'd already sent the ack in response to the
request.

libraries/GCS_MAVLink/GCS_Common.cpp

@@ -791,10 +791,6 @@ bool GCS_MAVLINK::should_send_message_in_delay_callback(const ap_message id) con
     // No ID we return true for may take more than a few hundred
     // microseconds to return!
 
-    if (id == MSG_HEARTBEAT || id == MSG_NEXT_PARAM) {
-        return true;
-    }
-
     if (in_hil_mode()) {
         // in HIL we need to keep sending servo values to ensure
         // the simulator doesn't pause, otherwise our sensor
@@ -805,6 +801,15 @@ bool GCS_MAVLINK::should_send_message_in_delay_callback(const ap_message id) con
         }
     }
 
+    switch (id) {
+    case MSG_HEARTBEAT:
+    case MSG_NEXT_PARAM:
+    case MSG_AUTOPILOT_VERSION:
+        return true;
+    default:
+        return false;
+    }
+
     return false;
 }