Set privacy mode to device mode in LL.

[pan-]

Do not enable address resolution when a new entry is added.

Summary of changes

Ensure LL resolution operates in device mode, not network mode as this is handled above.
Prevent activation of LL resolution when an entry is added.

This works around a Cordio LL bug which apply address resolution and Network mode filtering even if LL resolution is disabled.

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Impact of changes

Migration actions required

Documentation

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Pull request type

[] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

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Test results

[] No Tests required for this change (E.g docs only update)
[] Covered by existing mbed-os tests (Greentea or Unittest)
[] Tests / results supplied as part of this PR

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Reviewers

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[ciarmcom]

@pan-, thank you for your changes.
@ARMmbed/mbed-os-maintainers please review.