libbinder: Prettier initializer for bitset field

    size_t mMaxThreads = 1;

    std::optional<uint32_t> mProtocolVersion;

    // A mode is supported if the N'th bit is on, where N is the mode enum's value.

    std::bitset<8> mSupportedFileDescriptorTransportModes =

            (1 << static_cast<unsigned long>(RpcSession::FileDescriptorTransportMode::NONE));

    std::bitset<8> mSupportedFileDescriptorTransportModes = std::bitset<8>().set(

            static_cast<size_t>(RpcSession::FileDescriptorTransportMode::NONE));

    base::unique_fd mServer; // socket we are accepting sessions on

    std::mutex mLock; // for below