Not sure what you mean by "connection limit to the socket"
I'm guessing that you want to tweak a Linux/Unix box to scale up a bit better. If so, you can set the ulimit parameters and increase the soft and hard limits on the open files (nofiles . . . meaning, "number of files") and also expanding the allowable TCP socket number allowed to connect to the machine, for a particular user.
Google "sysctl ulimit scaling" and you'll find a bunch. Make sure it's associated with the openfire account (or whichever account is used to run your openfire instance).