Add case to test 802.1q vlan in guest

1. VIRT-95961 [virtual network][virtual-nic-device] Test 802.1q vlan in
guest
2. All the function doc string from Gemini CLI

Signed-off-by: Lei Yang <[email protected]>

Author: yanglei-rh

libvirt/tests/cfg/virtual_network/qemu/vlan.cfg

@@ -0,0 +1,36 @@
+- virtual_network.qemu_test.vlan: image_copy
+    type = vlan
+    # subnet should not be used by host
+    create_vm_libvirt = yes
+    kill_vm_libvirt = yes
+    master_images_clone = img1
+    main_vm = avocado-vt-vm1
+    subnet = "192.168"
+    vlan_num = 5
+    file_size = 10
+    maximal = 4094
+    listen_cmd = "nc -l %s > %s"
+    send_cmd = "nc %s %s < %s"
+    vms += " vm2"
+    cmd_type = ip
+    stop_firewall_cmd = "systemctl stop firewalld || service firewalld stop"
+    load_8021q_cmd = "modprobe 8021q"
+    msg_pattern = '8021q: Invalid VLAN id'
+    RHEL.7, ALT.7, RHEL.6:
+        msg_pattern = 'RTNETLINK answers: Numerical result out of range'
+    Windows:
+        # two windows VM, need more time to boot and login
+        only virtio_net
+        login_timeout = 720
+        vlan_num = 1
+        win_vlan_id = 900
+        cdroms += " virtio"
+        driver_verifier = netkvm
+        set_vlan_cmd = powershell -command "Set-NetAdapter -Name '%s' -VlanID ${win_vlan_id} -Confirm:$False"
+        Win2016, Win2019, Win8..1, Win2012..r2:
+                driver_verifier += " ndis"
+    variants:
+        - @vlan_connective_test:
+        - vlan_scalability_test:
+            only Linux
+            do_maximal_test = yes