docs/k8s: don't run subnet router in userspace mode (#11363)

There should not be a need to do that unless we run on host network

Signed-off-by: Irbe Krumina <irbe@tailscale.com>

docs/k8s/subnet.yaml

@@ -17,7 +17,9 @@ spec:
     - name: TS_KUBE_SECRET
       value: "{{TS_KUBE_SECRET}}"
     - name: TS_USERSPACE
-      value: "true"
+      value: "false"
+    - name: TS_DEBUG_FIREWALL_MODE
+      value: auto
     - name: TS_AUTHKEY
       valueFrom:
         secretKeyRef: