Build failure on 23.05 branch (ramips): nf_conntrack_ecache.c compile error

[sidpixel]

I encountered a build error when compiling the 23.05 branch for the ramips architecture.
It looks similar to unused symbol issues

Environment:

• Repo: lienol/openwrt (23.05)
• Target: ramips & x86
• Toolchain: default build system
• Host OS: Ubuntu 22.04 & 24.04

Error message:

CC net/8021q/vlanproc.o
AR net/8021q/built-in.a
AR net/wireless/built-in.a
CC net/switchdev/switchdev.o
AR net/switchdev/built-in.a
CC [M] net/netfilter/nf_conntrack_ecache.o
net/netfilter/nf_conntrack_ecache.c:136:12: error: '__nf_conntrack_eventmask_report' defined but not used [-Werror=unused-function]
136 | static int __nf_conntrack_eventmask_report(struct nf_conntrack_ecache *e,
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
make[7]: *** [scripts/Makefile.build:289: net/netfilter/nf_conntrack_ecache.o] Error 1
make[6]: *** [scripts/Makefile.build:552: net/netfilter] Error 2
make[5]: *** [Makefile:1927: net] Error 2
make[5]: Leaving directory '/mnt/src/openwrt/build_dir/target-mipsel_24kc_musl/linux-ramips_mt7621/linux-5.15.189'
make[4]: *** [Makefile:23: /mnt/src/openwrt/build_dir/target-mipsel_24kc_musl/linux-ramips_mt7621/linux-5.15.189/.modules] Error 2
make[4]: Leaving directory '/mnt/src/openwrt/target/linux/ramips'
make[3]: *** [Makefile:11: compile] Error 2
make[3]: Leaving directory '/mnt/src/openwrt/target/linux'
time: target/linux/compile#72.86#7.55#79.13
ERROR: target/linux failed to build.
make[2]: *** [target/Makefile:32: target/linux/compile] Error 1
make[2]: Leaving directory '/mnt/src/openwrt'
make[1]: *** [target/Makefile:25: /mnt/src/openwrt/staging_dir/target-mipsel_24kc_musl/stamp/.target_compile] Error 2
make[1]: Leaving directory '/mnt/src/openwrt'
make: *** [/mnt/src/openwrt/include/toplevel.mk:233: world] Error 2