Use 1MB as the max payload size in benchmarks to avoid exceeding Netty's buffer pool

default max buffer size.

benchmarks/src/jmh/java/io/grpc/benchmarks/netty/AbstractBenchmark.java

@@ -48,7 +48,9 @@ public abstract class AbstractBenchmark {
    * Standard payload sizes.
    */
   public enum PayloadSize {
-    SMALL(10), MEDIUM(1024), LARGE(65536), JUMBO(16777216);
+    // Max out at 1MB to avoid creating payloads larger than Netty's buffer pool can handle
+    // by default
+    SMALL(10), MEDIUM(1024), LARGE(65536), JUMBO(1048576);
 
     private final int bytes;
     PayloadSize(int bytes) {