STM32WL : add robustness

[jeromecoutant]

Summary of changes

Sometimes lorawan test was not 100% OK when it is executed many times.

@ludoch-stm
@hallard

Impact of changes

Migration actions required

Documentation

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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

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[ciarmcom]

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

[0xc0170]

Can you extend the commit message "add robustness" - where (is this lorawan), also what is this addressing - is there a bug or improvement?

[0xc0170]

I also wonder if we should document export deprecated feature

[0xc0170]

This should not be part of this PR neither the commit (not related to the PR ,is it?)

[jeromecoutant]

It's about WL... :-)
I could make 2 commits at least !

[0xc0170]

true lets separate these. Should we however document deprecated features (at least a note there ?)

[jeromecoutant]

@0xc0170 done

Pull request has been modified.

[0xc0170]

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[mbed-ci]

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