AP_Logger: add function to set longer log persist

libraries/AP_Logger/AP_Logger.cpp

@@ -1415,6 +1415,10 @@ bool AP_Logger::log_while_disarmed(void) const
 
     uint32_t now = AP_HAL::millis();
     uint32_t persist_ms = HAL_LOGGER_ARM_PERSIST*1000U;
+    if (_force_long_log_persist) {
+        // log for 10x longer than default
+        persist_ms *= 10U;
+    }
 
     // keep logging for HAL_LOGGER_ARM_PERSIST seconds after disarming
     const uint32_t arm_change_ms = hal.util->get_last_armed_change();

libraries/AP_Logger/AP_Logger.h

@@ -384,6 +384,7 @@ public:
 
     // accesss to public parameters
     void set_force_log_disarmed(bool force_logging) { _force_log_disarmed = force_logging; }
+    void set_long_log_persist(bool b) { _force_long_log_persist = b; }
     bool log_while_disarmed(void) const;
     uint8_t log_replay(void) const { return _params.log_replay; }
 
@@ -537,6 +538,7 @@ private:
 
     bool _writes_enabled:1;
     bool _force_log_disarmed:1;
+    bool _force_long_log_persist:1;
 
     // remember formats for replay
     void save_format_Replay(const void *pBuffer);