TCP sender waits 200ms to send data when receiver transmits small window

Issue

• Receiver application does connect(), or accept(), before calling setsockopt(SO_RCVBUF) to set SO_RCVBUF smaller than stream MSS. and smaller than maximum advertised window.
• TCP connection with:
  -- MSS larger than receiver advertised window
  -- receiver advertised window smaller than maximum advertised window
  -- sender waiting 200ms after receiving ACK before transmitting more payload.