TCPIP_SERVSOCKET(port) - Creates an listning socket.
Returns a handler that can be used with TCPIP_LISTEN
To then get each clients connection to this socket.
This runction returns handler to listning socket if
successfull else it returns -1.
Psychtoolbox/PsychHardware/iViewXToolbox/tcp_udp_ip/tcpip/tcpip_servsocket.m