T6267: Check interface wireless module before apply config

Check if the wireless device/modem exists in the system and the
module `ieee802111` was loaded
In cases where we do not have wireless devices, it prevents the
unexpected traceback

```
set interfaces wireless wlan0 address 192.0.2.5/32
commit

Traceback (most recent call last):
  File "/usr/libexec/vyos/conf_mode/interfaces_wireless.py", line 269, in <modu>
    c = get_config()
        ^^^^^^^^^^^^
  File "/usr/libexec/vyos/conf_mode/interfaces_wireless.py", line 104, in get_cg
    tmp = find_other_stations(conf, base, wifi['ifname'])
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/libexec/vyos/conf_mode/interfaces_wireless.py", line 54, in find_os
    for phy in os.listdir('/sys/class/ieee80211'):
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
FileNotFoundError: [Errno 2] No such file or directory: '/sys/class/ieee80211'
```

src/conf_mode/interfaces_wireless.py

@@ -1,6 +1,6 @@
 #!/usr/bin/env python3
 #
-# Copyright (C) 2019-2020 VyOS maintainers and contributors
+# Copyright (C) 2019-2024 VyOS maintainers and contributors
 #
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License version 2 or later as
@@ -48,9 +48,17 @@ def find_other_stations(conf, base, ifname):
     Only one wireless interface per phy can be in station mode -
     find all interfaces attached to a phy which run in station mode
     """
+    dict = {}
+    # Is class ieee80211 exists
+    if (
+        not os.path.isdir('/sys/class/ieee80211')
+        or len(os.listdir('/sys/class/ieee80211')) == 0
+    ):
+        return dict
+
     old_level = conf.get_level()
     conf.set_level(base)
-    dict = {}
+
     for phy in os.listdir('/sys/class/ieee80211'):
         list = []
         for interface in conf.list_nodes([]):
@@ -173,6 +181,13 @@ def verify(wifi):
             if len(wifi['station_interfaces'][phy]) > 0:
                 raise ConfigError('Only one station per wireless physical interface possible!')
 
+    # Wireless interface does not exist or module not loaded
+    if (
+        not os.path.isdir('/sys/class/ieee80211')
+        or len(os.listdir('/sys/class/ieee80211')) == 0
+    ):
+        raise ConfigError('Wireless module is not found!')
+
     verify_address(wifi)
     verify_vrf(wifi)
     verify_bond_bridge_member(wifi)