genCB = function(serverId) {
    return function(err) {
      if(err) {
        logger.error('[broadcast] fail to push message to serverId: ' + serverId + ', err:' + err.stack);
        latch.done();
        return;
      }
      successFlag = true;
      latch.done();
    };
  }
Broadcast message to all the connected clients.

@param  {String}   stype      frontend server type string
@param  {String}   route      route string
@param  {Object}   msg        message
@param  {Object}   opts       user-defined broadcast options, optional
                              opts.binded: push to binded sessions or all the sessions
                              opts.filterParam: parameters for broadcast filter.
@param  {Function} cb         callback
@memberOf ChannelService