Serial port pollution on startup

[Sonic-Amiga]

Despite redirection code, some serial log is still produced after serial port init. This causes delayed startup

[Sonic-Amiga]

The pollution comes from two facts:

1. Serial driver appears to buffer things internally; fflush() does not help

   ESP_LOGI (TAG, "Starting UART%s", s21 ? " S21" : "");
// Shut off console log if it is using our UART
#if defined(CONFIG_ESP_CONSOLE_UART_DEFAULT) || defined(CONFIG_ESP_CONSOLE_UART_CUSTOM_NUM_0)
   if (uart == UART_NUM_0) {
      fflush(stdout);
      esp_log_set_putchar(faikin_log_putc);
   }
#endif

"Starting UART" string already comes at 2400
2. wifi code inside the framework has its own dump, ignoring the putchar callback. espressif/ESP8266_RTOS_SDK#1082

[Sonic-Amiga]

Fixed by 6cb6279