fix: release dns_cache reference on timer rearm path

[PikuZheng]

Motivation

• Hourly-step memory increases were traced to dns_cache_expired() holding a dns_cache reference when the timeout callback returned UPDATE/RETRY and dns_timer_mod() was attempted but not accounted for, leading to transient retained references during concentrated expirations.
• The change ensures timer rearm failure cannot leave the timer-held cache reference unreleased so periodic cleanup (e.g. hourly maintenance) does not cause observable RSS step-ups.

Description

• Ensure dns_cache_release() is always called on the UPDATE/RETRY out path in src/dns_cache.c so a failed dns_timer_mod() does not omit releasing the held cache reference.
• Remove the unused mod_ret variable and simplify the dns_timer_mod() calls so the release is unconditional on the out path.
• Preserve existing behavior for the DEL and OK branches and only change the handling around timer rearm and release.

Testing

• Built the whole project with make -j2 and the build completed successfully.
• Recompiled the changed unit with make -C src dns_cache.o and the compilation completed successfully.

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Codex Task

[liouxunhuan8]

[edns.ipk]这个edns是代表什么版本？

[PikuZheng]

[edns.ipk]这个edns是代表什么版本？

编译时附加参数 CFLAGS="-DFEATURE_CHECK_EDNS"
据说是对上游的附加edns消息进行检查，如果上游没有返回正确的edns，则丢弃该查询结果（这是一个很久前遗留下来的，我也不知道是不是这样

[liouxunhuan8]

[edns.ipk]这个edns是代表什么版本？

编译时附加参数 CFLAGS=“-DFEATURE_CHECK_EDNS” 据说是对上游的附加edns消息进行检查，如果上游没有返回正确的edns，则丢弃该查询结果（这是一个很久前遗留下来的，我也不知道是不是这样

感谢解释

[liouxunhuan8]

最新的2026.v48.0.15
好像找不到aarch64-openwrt-edns.ipk
luci-compat-all.ipk 怎么整？

[PikuZheng]

最新的2026.v48.0.15 好像找不到aarch64-openwrt-edns.ipk luci-compat-all.ipk 怎么整？

编译失败了呗

[PikuZheng]

最新的2026.v48.0.15 好像找不到aarch64-openwrt-edns.ipk luci-compat-all.ipk 怎么整？

改好了