vlan与port的组织.一个系统中的port的数量在1K以内，

port以pid来标识，

pid分布在两个区间内，[0, 512]，[2048, 2048 + 128]，

port数量是一个固定值，启动时由系数检测，调用add_port()创建相应的数据结构-vlan and port organization. a system of port the number of 1K or less,

port the pid to identify,

pid distributed in two intervals, [0, 512], [2048, 2048+ 128],

port number is a fixed value, start by the coefficient of detection, call add_port () to create the corresponding data structure