km/common/ivm: rework piggy mac adress offset generation

For the the kmvect1 board we will also need a functionality to add an
offset to the IVMs MAC address, because these board will have two valid
ethernet ports for debugging purpose. So move the code to an own
function.

Signed-off-by: Holger Brunck <holger.brunck@keymile.com>
1 file changed