VTN Manager choose one active network interface in the host, and use the MAC address configured to that interface as identifier of the controller.

But current code contains two issues.

• If VMWare player is installed to the host, MAC address configured to
  a virtual network interface created by VMWare may be chosen as identifier
  though physical network interface is present in the host.
  MAC address of virtual network interface should not be used as controler
  identifier because it may conflict with another controller in the same cluster.

• MAC address configured to inactive network interface may be chosen
  though active network interface is present in the host.