Async IO test: add alt. setting for large number of small payloads.
Async IO test: add alt. setting for large number of small payloads.

This is useful to test backpressure TCP_NODELAY.

benmcclelland/kinetic-c,rcrane/kinetic-c,Kinetic/kinetic-c,kinjalcpatel/kinetic-c,benmcclelland/kinetic-c,kinjalcpatel/kinetic-c,chenchongli/kinetic-c,Kinetic/kinetic-c,Seagate/kinetic-c,Kinetic/kinetic-c,Kinetic/kinetic-c,Seagate/kinetic-c,benmcclelland/kinetic-c,rcrane/kinetic-c,benmcclelland/kinetic-c,kinjalcpatel/kinetic-c,kinjalcpatel/kinetic-c,chenchongli/kinetic-c,chenchongli/kinetic-c,Seagate/kinetic-c,chenchongli/kinetic-c,rcrane/kinetic-c,benmcclelland/kinetic-c,Seagate/kinetic-c,rcrane/kinetic-c