Function esp_openthread_get_dnsserver_addr 

pub unsafe extern "C" fn esp_openthread_get_dnsserver_addr(
    dnsserver_addr: *mut ip6_addr_t,
) -> esp_err_t

@brief This function acquires the main DNS server address for OpenThread netif.

@param[out] dnsserver_addr The dns server address.

@return - ESP_OK on sussess - ESP_ERR_INVALID_ARG if dnsserver_addr is NULL or obtained DNS server address is invalid - ESP_ERR_ESP_NETIF_IF_NOT_READY if openthread network interface is not initialized - ESP_ERR_ESP_NETIF_INVALID_PARAMS if failed to call esp_netif APIs getting dns info