IP_MTU
#if defined(OPENSSL_SYS_LINUX) && !defined(IP_MTU)
#if defined(OPENSSL_SYS_LINUX) && (defined(IP_MTU_DISCOVER) || defined(IP_MTU))
#if defined(OPENSSL_SYS_LINUX) && defined(IP_MTU)
if ((ret = getsockopt(b->num, IPPROTO_IP, IP_MTU, (void *)&sockopt_val,