Bug fix: Direct method subscription not removed after disconnect

[tmahmood-microsoft]

After a disconnect event, when the client reconnects, client subscribes to message receive event again resulting in multiple calls to direct method callback. The root cause was missing unsubscription after a disconnect event.

github issue: https://github.com/Azure/azure-iot-sdk-csharp/issues/3354

[tmahmood-microsoft]

/azp run

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[tmahmood-microsoft]

Updated and unhooking the message processor as a part of the transport handler's disconnection detection block.

[abhipsaMisra]

What scenarios did you test for this? Can we add some tests so that we don't regress in the future? For a unit test you could set up a mock client and trigger the disconnection event handler. Then, verify that the message processor handler was unhooked. As a bonus, you can also test that no other operation was executed on the client, i.e. no other handlers were attached or detached.

[tmahmood-microsoft]

/azp run

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[tmahmood-microsoft]

/azp run

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[tmahmood-microsoft]

/azp run

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Azure Pipelines successfully started running 1 pipeline(s).

[tmahmood-microsoft]

/azp run

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Azure Pipelines successfully started running 1 pipeline(s).

[tmahmood-microsoft]

/azp run

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Azure Pipelines successfully started running 1 pipeline(s).