Update Mbed CoAP to v5.1.7

[teetak01]

Summary of changes

Update Mbed CoAP to v5.1.7.

• Removed comparison of IP addresses when validating message resending. This avoids unnessary network errors due to load balancers causing frequent IP address changes.
• Multiple fixes for out-ouf-bounds memory accesses, a memory leak and an infinite loop condition in packet parser.
• Mapped MBED_CONF_MBED_CLIENT_RECONNECTION_COUNT Pelion Device Management Client configuration option to SN_COAP_RESENDING_MAX_COUNT in mbed-coap.
• Fix the token from blockwise ACK message to be empty if the received message doesn't have one.

Impact of changes

Migration actions required

Documentation

None

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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

[x] 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

@yogpan01 @anttiylitokola

[yogpan01]

@0xc0170 This fixes logical issues for PDMC when running with mbedOS 5.15 release branch versions. Please take this in the branch.

[ciarmcom]

@teetak01, thank you for your changes.
@yogpan01 @anttiylitokola @ARMmbed/mbed-os-maintainers please review.

[0xc0170]

CI started

[mbed-ci]

Test run: FAILED

Summary: 1 of 10 test jobs failed
Build number : 1
Build artifacts

Failed test jobs:

• jenkins-ci/mbed-os-ci_cloud-client-pytest-lts

[0xc0170]

I'l lrestart the entire pipeline latest tomorrow morning

[0xc0170]

CI restarted

[mbed-ci]

Test run: SUCCESS

Summary: 10 of 10 test jobs passed
Build number : 2
Build artifacts

[andypowers]

Approved.