Update mbed-coap to version 4.6.2

[anttiylitokola]

Description

Do not clear block2 in subsequent block request.

When sending a request with block2 option, eg. indicating need
for response to be blockwised, copy the block2 option from the
sent_blockwise list item so that the block2 option will be added
to all requests. This fixes an issue where previously the block2
was only sent for the first blockwise request and not for the
subsequent ones, including the last request. This made the response
not follow the request block2 option.

Pull request type

[X] Fix
[ ] Refactor
[ ] Target update
[ ] Functionality change
[ ] Breaking change

[anttiylitokola]

@kuggenhoffen, @yogpan01, please review.

[yogpan01]

Approved. @0xc0170 @cmonr please take this PR in for mbed-os-5.10 release.

[0xc0170]

We will start CI once the queue decreases slightly

[0xc0170]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 2951
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/7907/

Triggering tests

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

[mbed-ci]

Exporter Build : SUCCESS

Build number : 2567
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/7907/

[cmonr]

Reshuffling the Integration Test queue. Will restart shortly.

[mbed-ci]

Test : FAILURE

Build number : 2699
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/7907/2699

[NirSonnenschein]

/morph test

[0xc0170]

/morph test

[mbed-ci]

Test : FAILURE

Build number : 2747
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/7907/2747

[0xc0170]

/morph test

[mbed-ci]

Test : SUCCESS

Build number : 2749
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/7907/2749