PTNET_HDR_SIZE
unsigned int wanted_hdr_len = ptnet_vnet_hdr ? PTNET_HDR_SIZE : 0;
memset(nmbuf, 0, PTNET_HDR_SIZE);
nmbuf += PTNET_HDR_SIZE;
nmbuf_bytes += PTNET_HDR_SIZE;
if (unlikely(nmbuf_len < PTNET_HDR_SIZE)) {
nmbuf += PTNET_HDR_SIZE;
nmbuf_len -= PTNET_HDR_SIZE;