Sets level prefix for PhotonViews instantiated later on. Don't set it if you need only one!
Important: If you don't use multiple level prefixes, simply don't set this value. The default value is optimized out of the traffic. This won't affect existing PhotonViews (they can't be changed yet for existing PhotonViews). Messages sent with a different level prefix will be received but not executed. This affects RPCs, Instantiates and synchronization. Be aware that PUN never resets this value, you'll have to do so yourself.