ensures setupframe is available for future use (#1046)

Author: OlegDokuka

rsocket-core/src/main/java/io/rsocket/core/RSocketConnector.java

@@ -590,7 +590,7 @@ public Mono<RSocket> connect(Supplier<ClientTransport> transportSupplier) {
                                 dataMimeType,
                                 setupPayload);
 
-                        sourceConnection.sendFrame(0, setupFrame.retain());
+                        sourceConnection.sendFrame(0, setupFrame.retainedSlice());
 
                         return clientSetup
                             .init(sourceConnection)