openvpn can not detect kernel dco module

Hi:
    I want to try openvn dco at openwrt. the official openwrt
distribution stay at openvpn 2.5. so I tried compiled 2.6 and found it
can not find kernel dco module. I thought  maybe the distributed dco
module is too old so I compiled lasted kmod_ovpn_dco_v2 module but
"openvpn --version" still report: "DCO version: N/A".

    I compare the behavior with RHEL9. and I found if dco module is
not loaded, then "openvpn --version" will report "DCO version: N/A".
but if the dco module is loaded, "openvpn --version" should report
like "DCO version: copr:0.2.20231117-1.el9"
I don't know what to check. should I tune the compile parameters of
openvpn or the dco module?

below is the result under openwrt:

root@OpenWrt:~# lsmod | grep dco
ip6_udp_tunnel          1824  1 ovpn_dco_v2
ovpn_dco_v2            41056  0
udp_tunnel             10640  1 ovpn_dco_v2
root@OpenWrt:~# openvpn --version
OpenVPN 2.6.10 mipsel-openwrt-linux-gnu [SSL (OpenSSL)] [LZO] [LZ4]
[EPOLL] [MH/PKTINFO] [AEAD] [DCO]
library versions: OpenSSL 3.0.13 30 Jan 2024, LZO 2.10
DCO version: N/A
Originally developed by James Yonan
Copyright (C) 2002-2024 OpenVPN Inc <[email protected]>
Compile time defines: enable_async_push=no enable_comp_stub=no
enable_crypto_ofb_cfb=yes enable_dco=yes enable_dco_arg=yes
enable_debug=no enable_dependency_tracking=no enable_dlopen=unknown
enable_dlopen_self=unknown enable_dlopen_self_static=unknown
enable_fast_install=yes enable_fragment=yes enable_iproute2=no
enable_libtool_lock=yes enable_lz4=yes enable_lzo=yes
enable_management=no enable_nls=no enable_pam_dlopen=no
enable_pedantic=no enable_pkcs11=no enable_plugin_auth_pam=no
enable_plugin_down_root=no enable_plugins=no enable_port_share=yes
enable_selinux=no enable_shared=yes
enable_shared_with_static_runtimes=no enable_small=no
enable_static=yes enable_strict=no enable_strict_options=no
enable_systemd=no enable_werror=no enable_win32_dll=yes
enable_wolfssl_options_h=yes enable_x509_alt_username=no
with_aix_soname=aix with_crypto_library=openssl with_gnu_ld=yes
with_mem_check=no with_openssl_engine=no with_sysroot=no