Add IPv6 and VLAN devices to the web UI and router-setup

The web UI lists physical and VLAN interfaces and takes a VLAN uplink as
a device name (enp2s0.1001); it has IPv6 checkboxes for the WAN and each
LAN. router-setup asks whether to create VLANs before WAN and LAN are
picked, and whether to enable IPv6. --config-only writes the
configuration without installing, which the setup test uses for a PPPoE
uplink on a VLAN.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AeFqV9dZrK6nipHkPfyM4F

pkgs/router-webui/main.go

@@ -445,6 +445,7 @@ type networkData struct {
 	Form       Form
 	Errors     FormErrors
 	Interfaces []string
+	Devices    []Device
 }
 
 func (a *app) networkPage(w http.ResponseWriter, r *http.Request, sess session) {
@@ -457,7 +458,7 @@ func (a *app) networkPage(w http.ResponseWriter, r *http.Request, sess session)
 	}
 	f := s.form()
 	f.LANs = append(f.LANs, LANForm{DHCP: true}) // a row to add a LAN
-	p.Data = networkData{Form: f, Interfaces: Interfaces()}
+	p.Data = networkData{Form: f, Interfaces: Interfaces(), Devices: f.devices(Interfaces())}
 	a.render(w, "network", p)
 }
 
@@ -468,7 +469,7 @@ func formFromRequest(r *http.Request) Form {
 			Interface:     strings.TrimSpace(r.PostFormValue("wan.interface")),
 			Type:          r.PostFormValue("wan.type"),
 			PPPoEUser:     r.PostFormValue("wan.pppoe.username"),
-			PPPoEVLAN:     r.PostFormValue("wan.pppoe.vlan"),
+			IPv6:          r.PostFormValue("wan.ipv6") == "on",
 			PPPoEPassword: r.PostFormValue("wan.pppoe.password"),
 		},
 	}
@@ -482,6 +483,7 @@ func formFromRequest(r *http.Request) Form {
 			Address:   v("address"),
 			Prefix:    v("prefix"),
 			Internet:  v("internet") == "on",
+			IPv6PD:    v("ipv6pd") == "on",
 			DHCP:      v("dhcp") == "on",
 			PoolStart: v("poolStart"),
 			PoolEnd:   v("poolEnd"),
@@ -507,7 +509,7 @@ func (a *app) network(w http.ResponseWriter, r *http.Request, sess session) {
 		f.WAN.PPPoEPassword = ""
 		f.WAN.PasswordSet = s.form().WAN.PasswordSet
 		p.Error = "Please correct the marked fields."
-		p.Data = networkData{Form: f, Errors: fe, Interfaces: Interfaces()}
+		p.Data = networkData{Form: f, Errors: fe, Interfaces: Interfaces(), Devices: f.devices(Interfaces())}
 		w.WriteHeader(http.StatusUnprocessableEntity)
 		a.render(w, "network", p)
 		return