build failure for ESP32-C6 target

[lyusupov]

/home/codespace/Arduino/libraries/ArduinoBLE-1.3.7/src/utility/HCIVirtualTransport.cpp: In member function 'virtual int HCIVirtualTransportClass::begin()':
/home/codespace/Arduino/libraries/ArduinoBLE-1.3.7/src/utility/HCIVirtualTransport.cpp:83:10: error: 'struct esp_bt_controller_config_t' has no member named 'bluetooth_mode'
   83 |   bt_cfg.bluetooth_mode = ESP_BT_MODE_BLE; //different api for newer models
      |          ^~~~~~~~~~~~~~

esp_bt_controller_config_t type does no longer have bluetooth_mode member for C2, C6 and H2 targets:
https://github.com/espressif/esp-idf/blob/release/v5.2/components/bt/include/esp32c6/include/esp_bt.h#L166-L214

The PR #364 contains a proposed fix.

The ArduinoBLE library builds and boots fine on ESP32-C6 target afterwards.