If the network is already configured, the error text to that effect prints over the windows

[rminnich]

Describe the bug
if you start webboot, and exit, and start again, the net config will find out the net is already configured,
and print a message, but the message appears outside any text box

To Reproduce
start webboot, configure network, exit, start it again

Expected behavior
messages must always appear in a text box

[GBA-17]

I think some of the packages call fmt.Println(). One solution would be redirect stdout to a buffer, and then print the buffer contents in the error handler.