When an ethernet driver fails to send a frame we print an error in lwIP. But depending on how often that error is it might significantly delay transmissions. For example downloading a big file with the rpi4 spams the console with 'send error: -101', but removing the print makes the file download with an average speed of ~8.5MiB/s since the packets are retransmitted. So let's move it to a 'debug' in lwIP and expect ethernet drivers to handle the failure if it's severe. Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org> Reviewed-by: Jerome Forissier <jerome.forissier@linaro.org>