Fix shovel with AMQP 1.0 dest always being in flow state

[gomoripeti]

Proposed Changes

The link_state field should be under State.dest.current and the pending field should be under State.dest. Field being expected or put in the wrong place caused multiple function clauses not matching. Because of this the credited link event was never processed. But also a link_state=attached did not prevent messages to be forwarded. So the shovel accidentally worked fine.

I only tested manually, and did not even test when the shovel is really blocked and should cumulate some pending messages. Test cases need to be added, hence opening a draft PR.

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[michaelklishin]

The analysis looks correct to me. Thank you, @gomoripeti.