Build failure on MacOS:
=== Output from failing command(s) repeated here ===
* For target support_native_jdk.net_libextnet_MacOSXSocketOptions.o:
/Users/xueleifan/workspace/jdk-dev/src/jdk.net/macosx/native/libextnet/MacOSXSocketOptions.c:207:43: error: use of undeclared identifier 'IPV6_DONTFRAG'
        rv = setsockopt(fd, IPPROTO_IPV6, IPV6_DONTFRAG, &value, sizeof(value));
                                          ^
/Users/xueleifan/workspace/jdk-dev/src/jdk.net/macosx/native/libextnet/MacOSXSocketOptions.c:229:43: error: use of undeclared identifier 'IPV6_DONTFRAG'
        rv = setsockopt(fd, IPPROTO_IPV6, IPV6_DONTFRAG, &value, sizeof(value));
                                          ^
/Users/xueleifan/workspace/jdk-dev/src/jdk.net/macosx/native/libextnet/MacOSXSocketOptions.c:246:43: error: use of undeclared identifier 'IPV6_DONTFRAG'
        rv = getsockopt(fd, IPPROTO_IPV6, IPV6_DONTFRAG, &optval, &sz);
                                          ^
3 errors generated.

$ uname -a
Darwin XFans-MBP 21.6.0 Darwin Kernel Version 21.6.0: Mon Aug 22 20:19:52 PDT 2022; root:xnu-8020.140.49~2/RELEASE_ARM64_T6000 arm64