On my Linux Mint 19.1:
```bash
$ umask
0022
```

After the first run of `bitcoin-qt -sysperm=false` the `0700` permissions are expected for both the datadir (`~/.bitcoin`) and the walletdir (`~/.bitcoin/wallets`).

Actually, the directories are created with such access permissions:
```bash
$ stat ~/.bitcoin | grep Uid
Access: (0755/drwxr-xr-x)  Uid: ( 1000/ hebasto)   Gid: ( 1000/ hebasto)
$ stat ~/.bitcoin/wallets | grep Uid
Access: (0755/drwxr-xr-x)  Uid: ( 1000/ hebasto)   Gid: ( 1000/ hebasto)
```

Refs:
- #4286
- #13371
- #13389

NOTE: reading through the initial PR #4286 makes me think it was controversial. Is it a better and simpler way to just get rid of `-sysperm` option? I believe a user who needs this option can easily run `chown` command.
void AddWalletOptions(ArgsManager& argsman) const override;
    
    bool ParameterInteraction() const override;
    
    void Construct(NodeContext& node) const override;
};
void WalletInit::AddWalletOptions(ArgsManager& argsman) const
{
    argsman.AddArg("-addresstype", strprintf("What type of addresses to use (\"legacy\", \"p2sh-segwit\", \"bech32\", or \"bech32m\", default: \"%s\")", FormatOutputType(DEFAULT_ADDRESS_TYPE)), ArgsManager::ALLOW_ANY, OptionsCategory::WALLET);
    argsman.AddArg("-avoidpartialspends", strprintf("Group outputs by address, selecting many (possibly all) or none, instead of selecting on a per-output basis. Privacy is improved as addresses are mostly swept with fewer transactions and outputs are aggregated in clean change addresses. It may result in higher fees due to less optimal coin selection caused by this added limitation and possibly a larger-than-necessary number of inputs being used. Always enabled for wallets with \"avoid_reuse\" enabled, otherwise default: %u.", DEFAULT_AVOIDPARTIALSPENDS), ArgsManager::ALLOW_ANY, OptionsCategory::WALLET);
    argsman.AddArg("-changetype",
                   "What type of change to use (\"legacy\", \"p2sh-segwit\", \"bech32\", or \"bech32m\"). Default is \"legacy\" when "
                   "-addresstype=legacy, else it is an implementation detail.",
                   ArgsManager::ALLOW_ANY, OptionsCategory::WALLET);
    argsman.AddArg("-consolidatefeerate=<amt>", strprintf("The maximum feerate (in %s/kvB) at which transaction building may use more inputs than strictly necessary so that the wallet's UTXO pool can be reduced (default: %s).", CURRENCY_UNIT, FormatMoney(DEFAULT_CONSOLIDATE_FEERATE)), ArgsManager::ALLOW_ANY, OptionsCategory::WALLET);
    argsman.AddArg("-disablewallet", "Do not load the wallet and disable wallet RPC calls", ArgsManager::ALLOW_ANY, OptionsCategory::WALLET);
    argsman.AddArg("-discardfee=<amt>", strprintf("The fee rate (in %s/kvB) that indicates your tolerance for discarding change by adding it to the fee (default: %s). "
                                                                "Note: An output is discarded if it is dust at this rate, but we will always discard up to the dust relay fee and a discard fee above that is limited by the fee estimate for the longest target",
                                                              CURRENCY_UNIT, FormatMoney(DEFAULT_DISCARD_FEE)), ArgsManager::ALLOW_ANY, OptionsCategory::WALLET);
    argsman.AddArg("-fallbackfee=<amt>", strprintf("A fee rate (in %s/kvB) that will be used when fee estimation has insufficient data. 0 to entirely disable the fallbackfee feature. (default: %s)",
                                                               CURRENCY_UNIT, FormatMoney(DEFAULT_FALLBACK_FEE)), ArgsManager::ALLOW_ANY, OptionsCategory::WALLET);
    argsman.AddArg("-keypool=<n>", strprintf("Set key pool size to <n> (default: %u). Warning: Smaller sizes may increase the risk of losing funds when restoring from an old backup, if none of the addresses in the original keypool have been used.", DEFAULT_KEYPOOL_SIZE), ArgsManager::ALLOW_ANY, OptionsCategory::WALLET);
    argsman.AddArg("-maxapsfee=<n>", strprintf("Spend up to this amount in additional (absolute) fees (in %s) if it allows the use of partial spend avoidance (default: %s)", CURRENCY_UNIT, FormatMoney(DEFAULT_MAX_AVOIDPARTIALSPEND_FEE)), ArgsManager::ALLOW_ANY, OptionsCategory::WALLET);
    argsman.AddArg("-maxtxfee=<amt>", strprintf("Maximum total fees (in %s) to use in a single wallet transaction; setting this too low may abort large transactions (default: %s)",
        CURRENCY_UNIT, FormatMoney(DEFAULT_TRANSACTION_MAXFEE)), ArgsManager::ALLOW_ANY, OptionsCategory::DEBUG_TEST);
    argsman.AddArg("-mintxfee=<amt>", strprintf("Fee rates (in %s/kvB) smaller than this are considered zero fee for transaction creation (default: %s)",
                                                            CURRENCY_UNIT, FormatMoney(DEFAULT_TRANSACTION_MINFEE)), ArgsManager::ALLOW_ANY, OptionsCategory::WALLET);
    argsman.AddArg("-paytxfee=<amt>", strprintf("Fee rate (in %s/kvB) to add to transactions you send (default: %s)",