I don't see any information about this configuration parameter either DS admin guide or in the upstream ticket.

(In reply to Sankar Ramalingam from comment #1)
> I don't see any information about this configuration parameter either DS
> admin guide or in the upstream ticket.

A documentation bug will need to be opened for the Config/Command Guide.  Details on the listen queue backlog can be found in the manpage for listen (man 2 listen):

       int listen(int sockfd, int backlog);

  DESCRIPTION
       listen()  marks  the  socket referred to by sockfd as a passive socket,
       that is, as a socket that will be used to  accept  incoming  connection
       requests using accept(2).

       The  sockfd  argument  is  a file descriptor that refers to a socket of
       type SOCK_STREAM or SOCK_SEQPACKET.

       The backlog argument defines the maximum length to which the  queue  of
       pending  connections  for  sockfd  may  grow.   If a connection request
       arrives when the queue is full, the client may receive an error with an
       indication  of  ECONNREFUSED  or,  if  the underlying protocol supports
       retransmission, the request may be ignored so that a later reattempt at
       connection succeeds.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

http://rhn.redhat.com/errata/RHBA-2013-1653.html