MQTT-Kafka qos2: increasing tracked producer sequence number without publishing to Kafka

[bmaidics]

To Reproduce
Steps to reproduce the behavior:

1. Start zilla latest develop with mqtt.kafka.broker config
2. ./emqtt_bench pub -t t -c 2 -L 4 -I 100 -p 7183 --prefix test -q 2
3. benchmark fails, wireshark shows: invalid message as a Kafka produce response

Expected behavior
emqtt benchmark for qos2 publish should succeed