Fix flash bugs: remove netplan wifi conflict, suppress eth default route, force IPv4 for Tailscale install

- Remove 20-wifi.yaml netplan block (Bug 1): causes netplan to spawn its own wpa_supplicant instance, which claims ctrl_iface and blocks wpa_supplicant@wlan0.service. The per-interface systemd service is the correct approach.
- Add cleanup line to remove any pre-existing 20-wifi.yaml from the Armbian image.
- Patch 10-dhcp-all-interfaces.yaml to suppress default route on ethernet (Bug 2): without this, ethernet DHCP default route metric 100 beats WiFi metric 1024, routing internet traffic to ethernet which has no upstream. Causes Tailscale and firstboot to fail.
- Force IPv4 resolution in Tailscale curl (Bug 3): some homelab/ISP networks lack IPv6 internet routes. IPv6 DNS resolution for tailscale.com causes immediate curl failure on first boot.

operator_setup.sh

@@ -482,21 +482,8 @@ section "Applying Configuration"
 if [[ -n "$WIFI_SSID" ]]; then
     step "Writing WiFi profile..."
 
-    # Netplan config (primary — renderer: networkd)
+    # Remove any netplan wifi config — conflicts with wpa_supplicant@wlan0.service
-    mkdir -p "${MOUNT_POINT}/etc/netplan"
+    rm -f "${MOUNT_POINT}/etc/netplan/20-wifi.yaml"
-    cat > "${MOUNT_POINT}/etc/netplan/20-wifi.yaml" << EOF
-network:
-  version: 2
-  renderer: networkd
-  wifis:
-    wlan0:
-      dhcp4: yes
-      dhcp6: no
-      access-points:
-        "${WIFI_SSID}":
-          password: "${WIFI_PASS}"
-EOF
-    chmod 600 "${MOUNT_POINT}/etc/netplan/20-wifi.yaml"
 
     # wpa_supplicant direct config (backup — used by wpa_supplicant@wlan0.service)
     mkdir -p "${MOUNT_POINT}/etc/wpa_supplicant"
@@ -543,6 +530,28 @@ EOF
     info "WiFi profile written (SSID: ${WIFI_SSID})"
 fi
 
+# Patch ethernet netplan config to suppress default route
+step "Patching ethernet netplan config..."
+mkdir -p "${MOUNT_POINT}/etc/netplan"
+cat > "${MOUNT_POINT}/etc/netplan/10-dhcp-all-interfaces.yaml" << 'EOF'
+# Added by Armbian (modified: suppress default route on ethernet)
+network:
+  version: 2
+  renderer: networkd
+  ethernets:
+    all-eth-interfaces:
+      match:
+        name: "e*"
+      dhcp4: yes
+      dhcp6: yes
+      ipv6-privacy: yes
+      dhcp4-overrides:
+        use-routes: false
+      dhcp6-overrides:
+        use-routes: false
+EOF
+info "Ethernet netplan patched"
+
 # Root password
 step "Setting root password..."
 ROOT_PASS_HASH=$(openssl passwd -6 "$ROOT_PASS")
@@ -729,7 +738,7 @@ fi
 # VPN setup
 if [[ "${BB_VPN:-}" == "tailscale" && -n "${BB_TAILSCALE_KEY:-}" ]]; then
     echo "[*] Installing Tailscale..."
-    curl -fsSL https://tailscale.com/install.sh | sh
+    curl -4 -fsSL https://tailscale.com/install.sh | sh
     echo "[*] Connecting to Tailscale..."
     tailscale up --auth-key="${BB_TAILSCALE_KEY}" --accept-routes || echo "[-] Tailscale auth failed"
     # Remove auth key from config after use