Add Wi-SUN Interface APIs

[debdeep-arm]

Summary of changes

Implemented
-info_get API for Wi-SUN router to get RPL information.
-info_get API for Wi-SUN BR to get RPL information.
-routing_table_get API for Wi-SUN BR.

This is upstreaming PR #13084.

Impact of changes

Migration actions required

Documentation

None

Pull request type

[] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[X] 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

@mikter @mikaleppanen @artokin @ARMmbed/wi-sun-india

[ciarmcom]

@debdeep-arm, thank you for your changes.
@artokin @mikaleppanen @mikter @ARMmbed/mbed-os-ipcore @ARMmbed/mbed-os-maintainers please review.

[0xc0170]

Note, we are about to code freeze 6.1 . If this shall be in this release, should be reviewed asap.

[0xc0170]

CI started

[mbed-ci]

Test run: SUCCESS

Summary: 7 of 7 test jobs passed
Build number : 1
Build artifacts

[0xc0170]

Feature update

@debdeep-arm No docs update needed ? Just checking to be certain this has not missed any docs update.

[debdeep-arm]

Feature update

@debdeep-arm No docs update needed ? Just checking to be certain this has not missed any docs update.

No docs update required for this PR.