Motivation:
If the MQTT client specifies Subscribe Options parameters only available in MQTT v5 and tries to encode the message as MQTT v3 then an invalid QoS value is encoded
Modification:
Check MQTT version when encoding SUBSCRIBE message options, if it's 3.1 or 3.1.1 - only encode QoS, skip other options.
Result:
MqttEncoder produces a valid SUBSCRIBE message even if the client has specified options not available in the current MQTT version.
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