[php-src] Issue #20752: SNMP::__construct() fails to resolve hostname with warning "Unknown failure while resolving hostname"

Issue: https://github.com/php/php-src/issues/20752
Author: dshovchko

### Description

The following code:

```php
<?php

$session = new SNMP(SNMP::VERSION_2c, '127.0.0.1', 'public');
var_dump($session);
```

Resulted in this output:
```
PHP Warning:  SNMP::__construct(): Unknown failure while resolving '127.0.0.1' in /tmp/snmp_create_session.php on line 3
object(SNMP)#1 (8) {
  ["info"]=>
  array(3) {
    ["hostname"]=>
    string(0) ""
    ["timeout"]=>
    int(-1)
    ["retries"]=>
    int(-1)
  }
  ["max_oids"]=>
  NULL
  ["valueretrieval"]=>
  int(0)
  ["quick_print"]=>
  bool(false)
  ["enum_print"]=>
  bool(false)
  ["oid_output_format"]=>
  int(0)
  ["oid_increasing_check"]=>
  bool(false)
  ["exceptions_enabled"]=>
  int(0)
}
```

But I expected this output instead:
```
object(SNMP)#1 (8) {
  ["info"]=>
  array(3) {
    ["hostname"]=>
    string(9) "127.0.0.1"
    ["timeout"]=>
    int(-1)
    ["retries"]=>
    int(-1)
  }
  ["max_oids"]=>
  NULL
  ["valueretrieval"]=>
  int(0)
  ["quick_print"]=>
  bool(false)
  ["enum_print"]=>
  bool(false)
  ["oid_output_format"]=>
  int(0)
  ["oid_increasing_check"]=>
  bool(true)
  ["exceptions_enabled"]=>
  int(0)
}
```

The problem reproduces on `8.5.1`, `8.4.16`, and `8.4.15`.

### PHP Version

```plain
PHP 8.4.15 (cli) (built: Dec 11 2025 18:42:43) (NTS)
Copyright (c) The PHP Group
Zend Engine v4.4.15, Copyright (c) Zend Technologies
    with Zend OPcache v8.4.15, Copyright (c), by Zend Technologies

PHP 8.5.1 (cli) (built: Dec 21 2025 12:04:55) (NTS)
Copyright (c) The PHP Group
Zend Engine v4.5.1, Copyright (c) Zend Technologies
    with Zend OPcache v8.5.1, Copyright (c), by Zend Technologies
```

### Operating System

Ubuntu 24.04.3 LTS