Function esp_wifi_get_band 

pub unsafe extern "C" fn esp_wifi_get_band(band: *mut u32) -> i32

@brief Get WiFi current band.

@param[in] band store current band of WiFi

@return

• ESP_OK: succeed
• ESP_ERR_WIFI_NOT_INIT: WiFi is not initialized by esp_wifi_init
• ESP_ERR_INVALID_ARG: invalid argument