Update statement on decompression location

The docs state]: 

 "Kafka supports this with an efficient batching format. A batch of messages can be clumped together compressed and sent to the server in this form. This batch of messages will be written in compressed form and will
   remain compressed in the log and will only be decompressed by the consumer."

However, brokers always perform some amount of batch decompression in order to validate data. Internally, the LogValidator class implements the validation logic, and message decompression ultimately happens in the relevant CompressionType's wrapForInput implementation. These lines need updating to reflect that, including the scenarios that require full payload decompression on the broker (compacted topic, or topic level compression codec different from producer's codec).