lwip2.0.2 netbuf_new——分配netbuf结构体的内存. netbuf_alloc,分配netbuf中pbuf内存(pbuf_alloc中PBUF_RAM类型,包括pbuf结构体和payload区),如果使用nefbuf_ref的话,则不需要此步 netbuf_ref,分配netbuf中pbuf内存(pbuf_alloc中PBUF_REF类型,包括pbuf结构体,无payload区) netbuf_free,调用的是pbuf_free netbuf_delete,删除nef_b