BLE: Add MTU events

[paul-szczepanek-arm]

Description

Added events in the gap event handler to inform the user of ATT_MTU and packet payload size changes.

Pull request type

[ ] Fix
[ ] Refactor
[ ] Target update
[x] Functionality change
[ ] Docs update
[ ] Test update
[ ] Breaking change

Reviewers

Release notes

This adds optional events for informing the user of MTU changes and an option to attempt an MTU negotiation.

There is no effect on existing users; the usage is optional and will not affect users who don't use it. There is no migration path because the events are a new feature.

[pan-]

Could you document the ATT MTU and DLE behaviour ? When is it triggered automatically, when it is not ? It would be better to offer a consistent behaviour across ports. If we can't this must be documented.

[cmonr]

@pan- All good with the updates?

[pan-]

@cmonr I resolved what has been solved and left open what is not yet solved.

[paul-szczepanek-arm]

I rerouted the event handling to gatt server and and client - this is tentative, must review on Monday

[NirSonnenschein]

@pan- , some additional changes here, can you please review the latest changes.

[paul-szczepanek-arm]

@0xc0170 the system is not satisfied with Vincent's review sadly, can you help, please?

[0xc0170]

Please add Release notes to the first comment, following https://os.mbed.com/docs/mbed-os/v5.11/contributing/workflow.html#functionality-change

[0xc0170]

add SPDX identifier to all new files please

[paul-szczepanek-arm]

thanks - added

[0xc0170]

@AnotherButler Please review

[0xc0170]

CI restarted

[mbed-ci]

Test run: FAILED

Summary: 1 of 8 test jobs failed
Build number : 6
Build artifacts

Failed test jobs:

• jenkins-ci/mbed-os-ci_build-ARM

[paul-szczepanek-arm]

looking at the logs looks like CI failure to me

Loading library mbed-os-ci@master
java.io.FileNotFoundException: https://api.github.com/repos/ARMmbed/mbed-os-ci
	at com.squareup.okhttp.internal.huc.HttpURLConnectionImpl.getInputStream(HttpURLConnectionImpl.java:243)
	at com.squareup.okhttp.internal.huc.DelegatingHttpsURLConnection.getInputStream(DelegatingHttpsURLConnection.java:210)
	at com.squareup.okhttp.internal.huc.HttpsURLConnectionImpl.getInputStream(HttpsURLConnectionImpl.java:25)
	at org.kohsuke.github.Requester.parse(Requester.java:617)
	at org.kohsuke.github.Requester.parse(Requester.java:599)
	at org.kohsuke.github.Requester._to(Requester.java:277)
Caused: org.kohsuke.github.GHFileNotFoundException: {
  "message": "Server Error"
}

[cmonr]

Restarted CI

[mbed-ci]

Test run: SUCCESS

Summary: 12 of 12 test jobs passed
Build number : 7
Build artifacts