In legacy/trac#21530, we made relays exit if ExitRelay is auto, and either: * ReducedExitPolicy is 1, or * ExitPolicy is set But a relay operator who sets IPv6Exit to 1 also wants to be an exit. So we should add `IPv6Exit 1` to the options that activate exits when ExitRelay is auto. We should also update the documentation (see legacy/trac#29612).