Can't set TFTP server to listen to IPv6 in `os-tftp`

[kema-dev]

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Describe the bug A clear and concise description of what the bug is, including last known working version (if any).

• Can't set TFTP server to listen to IPv6 network.
• Clearly the same as https://github.com/opnsense/plugins/issues/4043 , superseeds https://github.com/opnsense/plugins/issues/4732

Tip: to validate your setup was working with the previous version, use opnsense-revert (https://docs.opnsense.org/manual/opnsense_tools.html#opnsense-revert)

To Reproduce Steps to reproduce the behavior:

1. Install os-tftp
2. Try to enable the server, making it listen to [::]

Expected behavior A clear and concise description of what you expected to happen.

• It just works

Screenshots If applicable, add screenshots to help explain your problem.

• See https://github.com/opnsense/plugins/issues/4043

Relevant log files If applicable, information from log files supporting your claim.

• See https://github.com/opnsense/plugins/issues/4043

Additional context Add any other context about the problem here.

• I suspect https://github.com/opnsense/plugins/blob/98c6d4b6368c291a3ba605edf888a237bec5801a/ftp/tftp/src/opnsense/mvc/app/models/OPNsense/Tftp/General.xml#L10 to be the culprit, not allowing IPv6 brackets. Did not test any fix, though.
• The workaround I found is to manually edit /etc/rc.conf.d/tftpd by adding the brackets (when inputting :: in web UI), then restarting tftpd via web UI.

Environment Software version used and hardware type if relevant.

• OPNsense 25.1.7_4 (amd64)