custom server.limit values are not used

[michel-laterman]

Loading agent limits (introduced in #1014) ignores any custom server.limits settings that are set in the fleet-ui and propagated to the fleet-server instance.

The fleet-server instance will receive the changed config and emit the "Re-configuring" message, however the configServerChagned comparison returns false

This is due to the LoadServerLimits() function overriding any server.limit.* config value is it uses the config blob returned by loadLimits().