page-xref: set ret to zero if PS_IO_FLUSH completed successfully

Due to this issue the server initiates closing a connection and its
socket is transfered into the TIME_WAIT state, so the second run of
page-server fails with the error "the address is already in use".
Signed-off-by: Andrew Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

page-xfer.c

@@ -197,6 +197,7 @@ static int page_server_serve(int sk)
 			}
 
 			flushed = true;
+			ret = 0;
 			break;
 		}
 		default: