Nimble still implements the legacy netdev API.
The `netdev_legacy_api` must be explicitly used, otherwise other network
drivers that use the new API will overwrite it also for nimble.
See #18426.
The `esptool.py` program is no longer installed as a RIOT package, but as a pure Python package, as published by Espressif. The installation takes place in a virtual Python environment in the `dist/tools/esptools/venv` directory. Therfore, there is no need to pull the GitHub repository and thus not necessary to install it as a RIOT package.
It makes no sense to have a separate `esp_ble_$(CPU_FAM)` feature for each ESP32x variant. The ESP32x has either a BLE controller or not. Therefore, a single common `esp_ble` feature is sufficient.
nimble_port_initialized` is false by default and is set to true as soon as
Adds a variable that indicates whether `nimble_port_init` has been called by `nimble_riot_init`, i.e. that the NimBLE stack has been initialized. The variable can be used to decide whether events from the low-level BLE controller driver should be forwarded to the NimBLE stack. It is necessary to avoid crashes in the case that the higher-prioritized thread of the low-level BLE controller driver starts sending events to the host before the NimBLE stack has been initialized by the lower-prioritized host thread.
BLE library for ESP32x implements its own version of `os_msys_init`, which is used by the BLE controller implementation for ESP32x and is implicitly called when the BLE controller is enabled.
BLE library for ESP32x defines its own `g_msys_pool_list` in binary libraries. To avoid multiple definitions, the definition of `g_msys_pool_list` is conditional here.
To be able to control whether `default_CSPNRG` is used or not during compilation, `define_RNG_default` is defined conditionally. This is needed for example to compile BLE for ESP32-H2.
The only function of the SPI flash driver part that is called by other parts of the package is `spi_enable_flash(0)` to disable the SPI flash during driver deinitialisation for power consumption reasons. Since we are not deinitialising the driver, the function is not called and can be commented out to compile the package without the SPI flash driver part.
