If we look at the way AddInterface() has been implemented, it will always create a virtualEndpoint, no matter the type of device backing the interface that we're trying to add. Unfortunately, this means neither vhost-user nor vfio can be leveraged in this case.

This needs to be fixed either by adding a new field devType to the grpc.Interface structure passed as an argument of AddInterface(), or by adding a new argument devType directly to the function itself.

@bergwolf @caoruidong @WeiZhang555 @amshinde WDYT?