EC_PKT_RDOFF
total_length = doff - EC_PKT_RDOFF;
buf += EC_PKT_RDOFF;
#define EC_PKT_MINRDOFF (EC_PKT_RDOFF + (ETHER_MIN_LEN - ETHER_CRC_LEN)) /* min packet doff (min size) */
#define EC_PKT_MAXRDOFF (EC_BUF_SZ - EC_PKT_RDOFF) /* max packet doff (max size) */