Fix DNS multiple query hints to perform both IP4 and IP6 tests

[tymoteuszblochmobica]

Multiple DNS Greentea tests fixed

Summary of changes

Getaddrinfo fails with IP6 interface due to hardcoded IP4 hints.
Replaced query hints with NSAPI_UNSPEC to perform both IP4 and IP6 .

Impact of changes

No impact

Migration actions required

Not needed

Documentation

Pull request type

[x] 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)
[x Covered by existing mbed-os tests (Greentea or Unittest)
[] Tests / results supplied as part of this PR

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Reviewers

@AnttiKauppila
@SeppoTakalo
@michalpasztamobica

[ciarmcom]

@tymoteuszblochmobica, thank you for your changes.
@AnttiKauppila @SeppoTakalo @michalpasztamobica @ARMmbed/mbed-os-test @ARMmbed/mbed-os-ipcore @ARMmbed/mbed-os-maintainers please review.

[michalpasztamobica]

Nice finding. This looks like a good explanation of why ip6 was failing and a well-targeted fix.

[0xc0170]

CI started

[mbed-ci]

Test run: SUCCESS

Summary: 5 of 5 test jobs passed
Build number : 1
Build artifacts