About struct in C

static struct rte_eth_conf port_conf = {
    .rxmode = {
        .mq_mode = ETH_MQ_RX_NONE,
        .max_rx_pkt_len = ETHER_MAX_LEN,
        .split_hdr_size = 0,
        .header_split = 0, /**< Header Split disabled */
        .hw_ip_checksum = 0, /**<IP checksum offload enabled */
        .hw_vlan_filter = 0, /**<VLAN filtering disabled */
        .jumbo_frame = 0, /**<Jumbo Frame Support disabled */
        .hw_strip_crc = 0, /**<CRC strip by hardware */
    },
    .rx_adv_conf = {
        .rss_conf = {
            .rss_key = NULL,
            .rss_hf = ETH_RSS_IP,
        },
    },
    .txmode = {
        .mq_mode = ETH_MQ_TX_NONE
    },
};