LRH_16B_BYTES
(LRH_16B_BYTES - LRH_9B_BYTES);
(LRH_16B_BYTES - LRH_9B_BYTES) + grh_len;
packet->payload = packet->ebuf + packet->hlen - LRH_16B_BYTES;
#define LRH_16B_DWORDS (LRH_16B_BYTES / sizeof(u32))