module handler decode error

[rigelrozanski]

Throughout the module handlers, unknown message types are returned with the error ErrTxDecode which is not necessarily correct, quoting @alexanderbez "somehow a message got routed incorrectly or the type is unsupported. It has nothing to do with tx decoding (at least not directly)."

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Acceptance Criteria

• Messages that are routed improperly should return an ErrUnknownRequest error