MACOS上面C/C++获取网卡索引，索引获取网卡接口名

依赖函数：

if_nametoindex   IF名字 to IF索引

if_indextoname   IF索引 to IF名字

MACOS 10.7 版本支援（就是2011年发不OSX的第一个面向用的系统版本）

        int GetInterfaceIndex(const ppp::string& ifrName) noexcept{if (ifrName.empty()){return -1;}int interface_index = (int)if_nametoindex(ifrName.data());if (interface_index == 0 || interface_index == -1){return -1;}return interface_index;}bool GetInterfaceName(int interface_index, ppp::string& ifrName) noexcept{ifrName.clear();if (interface_index == 0 || interface_index == -1){return false;}char buf[255];if (if_indextoname((unsigned int)interface_index, buf)){char ch = *buf;if (ch == '\x0'){return false;}ifrName = buf;return true;}else{return false;}}