This function causes pending outgoing data on connections to be sent, but unlike Update() it works when the server is not listening.
When the server is using externally added connections and the dontListen flag is set, the regular connection flush in the Update() function does not happen. In this case, UpdateConnections can be called to pump the external connections. This is an advanced usage that should not be required unless the server uses custom NetworkConnection classes that do not use the built-in transport layer.