Commit b00fae4ef8 for openssl.org

commit b00fae4ef89a4926f9122d1cf18cc26a9e8c213f
Author: Neil Horman <nhorman@openssl.org>
Date:   Mon Feb 2 18:46:49 2026 -0500

    Gate use of IPV6_PMTUDISC_PROBE on it being defined

    We accidentally introduced a use of IPV6_PMTUDISC_PROBE without checking
    if it was defined in
    https://github.com/openssl/openssl/pull/28809

    leading to build failures on systems that don't define it.  Fix that.

    Fixes #29903

    Reviewed-by: Eugene Syromiatnikov <esyr@openssl.org>
    Reviewed-by: Saša Nedvědický <sashan@openssl.org>
    MergeDate: Wed Feb  4 19:23:14 2026
    (Merged from https://github.com/openssl/openssl/pull/29927)

diff --git a/crypto/bio/bss_dgram.c b/crypto/bio/bss_dgram.c
index 28333aecc7..8ead293f0b 100644
--- a/crypto/bio/bss_dgram.c
+++ b/crypto/bio/bss_dgram.c
@@ -961,7 +961,7 @@ static long dgram_ctrl(BIO *b, int cmd, long num, void *ptr)
                 ERR_raise_data(ERR_LIB_SYS, get_last_socket_error(),
                     "calling setsockopt()");

-#elif defined(OPENSSL_SYS_LINUX) && defined(IPV6_MTU_DISCOVER)
+#elif defined(OPENSSL_SYS_LINUX) && defined(IPV6_MTU_DISCOVER) && defined(IPV6_PMTUDISC_PROBE)
             sockopt_val = num ? IPV6_PMTUDISC_PROBE : IPV6_PMTUDISC_DONT;
             if ((ret = setsockopt(b->num, IPPROTO_IPV6, IPV6_MTU_DISCOVER,
                      &sockopt_val, sizeof(sockopt_val)))