haddowk@ recently added support for statically assigning the moblab's sub-DUTs' mac-ip mapping. This ask is a step further -- 

we want to statically assign the mac address of the network interface that should be considered internal by moblab.

This is needed for moblab VM Test where there is no sensible way to distinguish between the two network interfaces and also for future of moblab where we may not use USB dongles for network interfaces at all.