chrony: add UCI options for drift file and time restoration

[drizt]

chronyd can restore the system time at startup from the drift file's modification time. This helps routers without a real-time clock recover a more recent time after reboot when the drift file is stored on persistent storage.

Add a UCI section to configure the drift file path, its minimum update interval, and optional time restoration using chronyd's -s option. Keep time restoration disabled by default and preserve the existing drift file path for configurations without the new section.

config driftfile 'driftfile'
    # Set to 1 to restore time from the drift file at startup
    option restore_time '0'
    # Use a path on persistent storage to retain the file across reboots
    option file '/var/run/chrony/drift'
    # Minimum update interval in seconds; empty uses chronyd's default
    option interval ''

📦 Package Details

Maintainer: @mlichvar
_{(You can find this by checking the history of the package Makefile.)}

Description:
See commit message

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🧪 Run Testing Details

• OpenWrt Version: 25.12.5 r33051-f5dae5ece4
• OpenWrt Target/Subtarget: ramips/mt7621
• OpenWrt Device: ASUS RT-AX53U

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✅ Formalities

• I have reviewed the CONTRIBUTING.md file for detailed contributing guidelines.

[openwrt]

Formality Check: Failed

We checked this pull request against the contribution guidelines. Here is what needs your attention:

🛑 CRITICAL ERRORS

Commit 429bef3 - chrony: add UCI options for drift file and time restoration:

• File 'net/chrony/files/chrony.conf' is destined for '/etc/config/' but is not a valid UCI configuration file. In OpenWrt, '/etc/config/' is reserved for UCI-formatted configuration files. Raw files (such as TOML, JSON, or YAML) are not allowed at this path. Invalid line 2: 'confdir /var/etc/chrony.d'

Tip

Do not close this pull request to make corrections. Instead, modify your existing commits (e.g. git commit --amend) and update the branch using git push --force-with-lease --force-if-includes. The checks will re-run automatically.

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_{Something broken? Consider reporting an issue.
Running version 37cc78e deployed on 2026-10-15 12:36:36 CEST}

[drizt]

File 'net/chrony/files/chrony.conf' is destined for '/etc/config/' but is not a valid UCI configuration file. In OpenWrt, '/etc/config/' is reserved for UCI-formatted configuration files. Raw files (such as TOML, JSON, or YAML) are not allowed at this path. Invalid line 2: 'confdir /var/etc/chrony.d'

It's not mine file. The file from original package. I only removed two lines in it.