Function start 

pub fn start<W>(buf: &mut [u8], write: W, uid: u32) -> Result<(), EspError>
where
    W: FnMut(&[u8]) -> Result<(), EspError>,

Start WiFi according to current configuration If mode is WIFI_MODE_STA, it creates station control block and starts station If mode is WIFI_MODE_AP, it creates soft-AP control block and starts soft-AP If mode is WIFI_MODE_APSTA, it creates soft-AP and station control block and starts soft-AP and station If mode is WIFI_MODE_NAN, it creates NAN control block and starts NAN. docs)