DNSSEC validation should not be enabled by default in v6

[DL6ER]

What does this implement/fix?

DNSSEC validation should not be enabled by default - it wasn't in v5, either. The reason for this is that it may be causing issues on devices with broken/missing RTCs where NTP time synchronization relies on DNS resolution

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Related issue or feature (if applicable): N/A

Pull request in docs with documentation (if applicable): N/A

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