8233296: MulticastSocket getOption/setOption inverts the value of IP_MULTICAST_LOOP Summary: MulticastSocket.getOption(StandardSocketOption.IP_MULTICAST_LOOP) now returns true if loopback mode is enabled, and MulticastSocket.setOption(StandardSocketOption.IP_MULTICAST_LOOP, true) enables loopback mode. No other behavioral changes. Reviewed-by: alanb, chegar

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