why fastopen failed from client perspective
pub const tcp_fastopen_client_fail = enum
pub const tcp_fastopen_client_fail = enum {
/// catch-all
TFO_STATUS_UNSPEC,
/// if not in TFO_CLIENT_NO_COOKIE mode
TFO_COOKIE_UNAVAILABLE,
/// SYN-ACK did not ack SYN data
TFO_DATA_NOT_ACKED,
/// SYN-ACK did not ack SYN data after timeout
TFO_SYN_RETRANSMITTED,
}