Update mbed-coap to version 4.4.0

[anttiylitokola]

Description

Make sn_coap_protocol_send_rst as public needed for CoAP ping sending
Allow disabling resendings by defining SN_COAP_DISABLE_RESENDINGS

Pull request type

• Fix
• Refactor
• New target
• Feature
• Breaking change

[anttiylitokola]

@yogpan01, @TeroJaasko please review.

[anttiylitokola]

@0xc0170, can you push this one into 5.8 release? We need to get this in to replace TCP keepalive socket option which might not be part of every socket implementation.

[yogpan01]

looks good. We need this feature to fix critical client error where it keeps dropping connection because there is no CoAP ping functionality to keep the connection alive.
@0xc0170 @adbridge Can this be accomodated for 5.8 release, if not then the next candidate. There is no API breaks introduced and change is transparent for any of the existing components so it is completely backward compatible and doesn't impact any exisitng functionality.
This PR will enable client to use this API on its end to fix connectivity interruptions.

[0xc0170]

/morph build

[0xc0170]

@0xc0170 @adbridge Can this be accomodated for 5.8 release, if not then the next candidate. There is no API breaks introduced and change is transparent for any of the existing components so it is completely backward compatible and doesn't impact any exisitng functionality.

Looking at the changes, it adds new API, by default this would be marked for 5.9

[yogpan01]

@0xc0170 These are internal changes required for cloud client. This has no direct relevance to any mbed-os functionality. This is C API anyway which we use internally to fix our keep alive logic which is completely cloud client internal logic. Because coap happens to be part of mbed-os and we need to extend this functionality there. You need to take exception for Cloud Client components to allow them to add extensions to their features.
We need this in next release patch, please.

[0xc0170]

This has no direct relevance to any mbed-os functionality. This is C API anyway which we use internally to fix our keep alive logic which is completely cloud client internal logic.

Labeled as such, thanks for the further information.

[mbed-ci]

Build : SUCCESS

Build number : 1485
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/6357/

Triggering tests

/morph test
/morph uvisor-test
/morph export-build
/morph mbed2-build

[mbed-ci]

Exporter Build : SUCCESS

Build number : 1130
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/6357/

[mbed-ci]

Test : SUCCESS

Build number : 1272
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/6357/1272

[adbridge]

This sits on top of coap 4.3 which is going to 5.9, so this also needs to go to 5.9!

[adbridge]

@yogpan01 if this contains a specific fix that is unrelated to the 4.3 coap release and needs to go to 5.8, then please create a PR again directly to that branch. We also need to revisit how this flow is working as it keeps breaking our release process...

[yogpan01]

@adbridge I dont get it how it breaks your release process ? I already provided explaination that these are internal API changes needed for client only, Also, these are C APIs only so according to mbedOS backward compatibility promise, this is not an issue for any customer as they don't see these directly.
Can this commit be cherry-picked to mbedOS 5.8.1 . I don't see why this require a separate PR from our side.

[yogpan01]

@adbridge If there is any issue of only picking this commit for 5.8.1 , please pick the #6171 as well. Both are perfectly fine to be cherry-picked for 5.8.1 with no breaking changes in them.

[yogpan01]

@adbridge @0xc0170 This is also required for 5.8.1