Add an update interval for client update packets

[JohnAFernandez]

Client update packets are sent from the server to client to update the health and threats on the hud. Currently, there is a one-size fits all interval of 333 ms. Very noticeable, especially at high pings (missile damage could show up half a second after impact, for instance). This was discovered while doing code analysis for the ETS refactor.

So if we've set a higher update rate in the multi options menu, allow for shorter interval times.