AP_Logger: do not log soon after file transfer unless we're armed

mavlink log reads fail randomly, and you end up with a very large number
of log files as we keep closing logs off and then discovering we should
be logging

libraries/AP_Logger/AP_Logger.h

@@ -554,6 +554,9 @@ private:
         SENDING, // actively sending log_sending packets
     } transfer_activity = TransferActivity::IDLE;
 
+    // last time we handled a log-transfer-over-mavlink message:
+    uint32_t _last_mavlink_log_transfer_message_handled_ms;
+
     // next log list entry to send
     uint16_t _log_next_list_entry;
 

libraries/AP_Logger/AP_Logger_Backend.cpp

@@ -429,6 +429,17 @@ bool AP_Logger_Backend::ShouldLog(bool is_critical)
         return false;
     }
 
+    if (_front._last_mavlink_log_transfer_message_handled_ms != 0) {
+        if (AP_HAL::millis() - _front._last_mavlink_log_transfer_message_handled_ms < 10000) {
+            if (!_front.vehicle_is_armed()) {
+                // user is transfering files via mavlink
+                return false;
+            }
+        } else {
+            _front._last_mavlink_log_transfer_message_handled_ms = 0;
+        }
+    }
+
     if (is_critical && have_logged_armed && !_front._params.file_disarm_rot) {
         // if we have previously logged while armed then we log all
         // critical messages from then on. That fixes a problem where

libraries/AP_Logger/AP_Logger_MAVLinkLogTransfer.cpp

@@ -45,6 +45,7 @@ void AP_Logger::handle_log_message(GCS_MAVLINK &link, const mavlink_message_t &m
     if (!should_handle_log_message()) {
         return;
     }
+    _last_mavlink_log_transfer_message_handled_ms = AP_HAL::millis();
     switch (msg.msgid) {
     case MAVLINK_MSG_ID_LOG_REQUEST_LIST:
         handle_log_request_list(link, msg);