Custom usb mode for [ace] which enables the rndis device

*grin* ... s/genius/mad genius/ maybe...

Lets remove the reason for such ... genius ... code:

If there is a %define enable_kernel_update <anything including 0> then it's defined.

If someone defines it to 0 thinking that's the same as undefined then that's a bug in either the docs or their .spec file. I don't want to support a full on javascript parse of what evaluates to false - we'll use defined/undefined for boolean :)