network: Assign "static" MAC addresses to QMI interfaces

network: Assign "static" MAC addresses to QMI interfaces

This is really badly hacky, but I do not know a better way to solve this
with our existing "setup" program which would be a nightmare to extend.

So we are using the device number to generate a static MAC address which
can then be used as usual. I doubt many people will have more than one
device.

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>