The matlabroot/toolbox/coder/rtiostream/src/rtiostreamtcpip/rtiostream_tcpip.c file shows how you can turn off Nagle's algorithm:
/* Disable Nagle's Algorithm*/
option = 1;
sockStatus = setsockopt(lFd,IPPROTO_TCP,TCP_NODELAY,(char*)&option,sizeof(option));
The code for your custom TCP/IP implementation can require modification.