Only check the size of indexed column values when they are of type KEYS

https://github.com/apache/cassandra/blob/cassandra-1.0.8/src/java/org/apache/cassandra/thrift/ThriftValidation.java#L431

That line states that: Indexed column values cannot be larger than 64K. But in some cases we would want the column values to be able to be larger than 64k, specifically if the index_type is not of type KEYS.