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.
break;
        default:
            to[i] = from[i];
            break;
        }
    }
    return to;
}
/**
 * Decode an I2P-style Base64 string.
 * @param[in] i2p_b64 I2P-style Base64 string.
 * @return decoded `i2p_b64`
 * @throw std::runtime_error if decoding fails
 */
static Binary DecodeI2PBase64(const std::string& i2p_b64)
{
    const std::string& std_b64 = SwapBase64(i2p_b64);
    auto decoded = DecodeBase64(std_b64);
    if (!decoded) {
        throw std::runtime_error(strprintf("Cannot decode Base64: \"%s\"", i2p_b64));
    }
    return std::move(*decoded);
}
/**
 * Derive the .b32.i2p address of an I2P destination (binary).
 * @param[in] dest I2P destination.
 * @return the address that corresponds to `dest`
 * @throw std::runtime_error if conversion fails
 */
static CNetAddr DestBinToAddr(const Binary& dest)