Updated to ignore all control batches

Control batches can show up even outside of transactions. This change
drops the requirement that you must be in a transaction for a record to
be labled a control batch.

Author: rkruze

lib/kafka/protocol/record_batch.rb

@@ -213,7 +213,7 @@ def self.decode(decoder)
       end
 
       def mark_control_record
-        if in_transaction && is_control_batch
+        if is_control_batch
           record = @records.first
           record.is_control_record = true unless record.nil?
         end