Modifying SSS example to use SOCK_DGRAM

I made a trivial change today to the Simple Socket Server example that comes with the altera software. I changed the SOCK_STREAM to SOCK_DGRAM. Now the listen() fails for some reason, but errno is 0?? Code and output are below.

  if ((fd_listen = socket(AF_INET, SOCK_DGRAM, 0)) < 0)  {
    alt_NetworkErrorHandler(EXPANDED_DIAGNOSIS_CODE," Socket creation failed");
  }
  addr.sin_family = AF_INET;
  addr.sin_port = htons(30);
  addr.sin_addr.s_addr = INADDR_ANY;
  if ((bind(fd_listen,(struct sockaddr *)&addr,sizeof(addr))) < 0)
  {
    alt_NetworkErrorHandler(EXPANDED_DIAGNOSIS_CODE," Bind failed");
  }
  
  if ((listen(fd_listen,1)) < 0)
  {
      printf("errno = %d\n", errno);
    alt_NetworkErrorHandler(EXPANDED_DIAGNOSIS_CODE," Listen failed");
  }
   

Created "Nios II Simple Socket Server" task (Prio: 10)

errno = 0

[Network]: See STDERR for expanded diagnosis translation.

[Network]: [SSS_task] Listen failed

[Network]: ERRNO: :

[Network]: See STDERR (FAULT_LEVEL is SYSTEM).

[Network]: FAULT_LEVEL is SYSTEM.

[Network]: FATAL Error, Restart required.

[Network]: Locking scheduler - endless loop.

No free buffers for rx

No free buffers for rx