mod_smacks: Fix some bugs with smacks-ack-delayed event triggering. The old code had several flaws which are addressed here. First of all this fixes the if statement guarding the event generation There where some timing glitches addressed by this commit as well.

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summary: Storage benchmark tool
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To benchmark `mod_storage_internal`:

    prosodyctl mod_benchmark_storage internal

Does a number (aprox. 10000) of reads and writes and to the selected
storage driver and tells you how long it took.