relay: Send back connection refused end reason on network reentry

The current used TORPROTOCOL end reason has a very bad side effect of killing the circuit on the client side and thus all the streams attached to it.

It is very bad if that would happen since anyone could just serve a HTTP resource in a page that would contact a relay on its ORPort and see that circuit collapsing.

Instead, send back CONNECTION_REFUSED so the circuit won't be used anymore but will not collapse.