#676 introduced client/server SocketAcceptor of same form (SetupFrame, RequesterRSocket) -> Mono<HandlerRSocket>, which deadlocks RSocket if both acceptors do e.g.
return RequesterRSocket.requestResponse(Payload).map(Payload -> HandlerRSocket). SocketAcceptor could be of form (SetupFrame, RequesterRSocket) -> HandlerRSocket on both sides (symmetric), with server signature (SetupFrame, RSocketRequester) -> Mono<SocketAcceptor>, and client signature just (SetupFrame, RSocketRequester) -> SocketAcceptor - as only server is able to reject requests