GCS_MAVLink: slow down telemetry during ftp

libraries/GCS_MAVLink/GCS.h

@@ -707,6 +707,7 @@ private:
         int fd = -1;
         FTP_FILE_MODE mode; // work around AP_Filesystem not supporting file modes
         int16_t current_session;
+        uint32_t last_send_ms;
     };
     static struct ftp_state ftp;
 

libraries/GCS_MAVLink/GCS_Common.cpp

@@ -847,6 +847,12 @@ uint16_t GCS_MAVLINK::get_reschedule_interval_ms(const deferred_message_bucket_t
         // we are sending requests for waypoints, penalize streams:
         interval_ms *= 4;
     }
+#if HAVE_FILESYSTEM_SUPPORT
+    if (ftp.replies && AP_HAL::millis() - ftp.last_send_ms < 500) {
+        // we are sending ftp replies
+        interval_ms *= 4;
+    }
+#endif
 
     if (interval_ms > 60000) {
         return 60000;

libraries/GCS_MAVLink/GCS_FTP.cpp

@@ -114,6 +114,7 @@ void GCS_MAVLINK::send_ftp_replies(void) {
                     0, reply.sysid, reply.compid,
                     payload);
                 ftp.replies->pop(reply);
+                ftp.last_send_ms = AP_HAL::millis();
         } else {
             return;
         }