创建虚拟的vlan设备
例如：
vconfig add eth0 10
就创建了一个eth0.10的设备
vconfig的使用说明如下：
root@hbg:/# vconfig
BusyBox v1.22.1 (2015-12-18 15:33:52 CST) multi-call binary.
Usage: vconfig COMMAND [OPTIONS]
Create and remove virtual ethernet devices
add IFACE VLAN_ID
rem VLAN_NAME
set_flag IFACE 0|1 VLAN_QOS
set_egress_map VLAN_NAME SKB_PRIO VLAN_QOS
set_ingress_map VLAN_NAME SKB_PRIO VLAN_QOS
set_name_type NAME_TYPE