code: func CreateVlanInterface(t *testing.T, master, slave, id string) {
  	// ip link add link <master> name <master>.<VID> type vlan id <VID>
  	icmd.RunCommand("ip", "link", "add", "link", master, "name", slave, "type", "vlan", "id", id).Assert(t, icmd.Success)
  	// ip link set <sub_interface_name> up
  	icmd.RunCommand("ip", "link", "set", slave, "up").Assert(t, icmd.Success)
  }
docs: // CreateVlanInterface creates a vlan network interface