Do not "exit" if boot option nonetworking is set but "return" instead

Do not "exit" if boot option nonetworking is set but "return" instead

Nowadays we're running under one main script which sources all
the further scripts. If we 'exit' in a script then we'd just exit
the main init sequence, resulting in a kernel trace because the
real™ init hasn't been found/executed.

Thanks to Florian Ermisch <floh.edo@googlemail.com> for the initial bug report