TCP_MIN_MSS
icsk->icsk_ack.rcv_mss = TCP_MIN_MSS;
if (val && (val < TCP_MIN_MSS || val > MAX_TCP_WINDOW))
(len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
hint = max(hint, TCP_MIN_MSS);
inet_csk(ssk)->icsk_ack.rcv_mss = TCP_MIN_MSS;