fix(helpers): attach Layer2VIP to VLAN interface in generic multi-doc path

Mirror of the cozystack fix: when the default link is a VLAN,
$interfaceName is rewritten to the parent link while the VLAN
addresses/routes are emitted on $defaultLinkName. Use $defaultLinkName
for Layer2VIPConfig.link in that branch so the VIP stays on the VLAN.

Address review feedback from coderabbitai on charts/generic/templates/_helpers.tpl:152.

Assisted-By: Claude <noreply@anthropic.com>
Signed-off-by: Aleksei Sviridkin <f@lex.la>

Author: lexfrei

charts/generic/templates/_helpers.tpl

@@ -144,12 +144,16 @@ addresses:
 routes:
   - gateway: {{ include "talm.discovered.default_gateway" . }}
 {{- end }}
+{{- $vipLinkName := $interfaceName }}
+{{- if $isVlan }}
+{{- $vipLinkName = $defaultLinkName }}
+{{- end }}
 {{- if and .Values.floatingIP (eq .MachineType "controlplane") }}
 ---
 apiVersion: v1alpha1
 kind: Layer2VIPConfig
 name: {{ .Values.floatingIP | quote }}
-link: {{ $interfaceName }}
+link: {{ $vipLinkName }}
 {{- end }}
 {{- end }}