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.
{
    
    
    
    static constexpr size_t DEST_LEN_BASE = 387;
    static constexpr size_t CERT_LEN_POS = 385;
    uint16_t cert_len;
    memcpy(&cert_len, &m_private_key.at(CERT_LEN_POS), sizeof(cert_len));
    cert_len = be16toh(cert_len);
    const size_t dest_len = DEST_LEN_BASE + cert_len;
    return Binary{m_private_key.begin(), m_private_key.begin() + dest_len};
}
void Session::CreateIfNotCreatedAlready()
{
    std::string errmsg;
    if (m_control_sock->IsConnected(errmsg)) {
        return;
    }
    const auto session_type = m_transient ? "transient" : "persistent";
    const auto session_id = GetRandHash().GetHex().substr(0, 10); 
    Log("Creating %s SAM session %s with %s", session_type, session_id, m_control_host.ToString());
    auto sock = Hello();
    if (m_transient) {