client/web: properly show "Log In" for web client on fresh install (#14569)

Change the type of the `IPv4` and `IPv6` members in the `nodeData`
struct to be `netip.Addr` instead of `string`.

We were previously calling `String()` on this struct, which returns
"invalid IP" when the `netip.Addr` is its zero value, and passing this
value into the aforementioned attributes.

This caused rendering issues on the frontend
as we were assuming that the value for `IPv4` and `IPv6` would be falsy
in this case.

The zero value for a `netip.Addr` marshalls to an empty string instead
which is the behaviour we want downstream.

Updates https://github.com/tailscale/tailscale/issues/14568

Signed-off-by: Mario Minardi <mario@tailscale.com>

client/web/web.go

@@ -804,8 +804,8 @@ type nodeData struct {
 	DeviceName  string
 	TailnetName string // TLS cert name
 	DomainName  string
-	IPv4        string
-	IPv6        string
+	IPv4        netip.Addr
+	IPv6        netip.Addr
 	OS          string
 	IPNVersion  string
 
@@ -864,10 +864,14 @@ func (s *Server) serveGetNodeData(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	filterRules, _ := s.lc.DebugPacketFilterRules(r.Context())
+	ipv4, ipv6 := s.selfNodeAddresses(r, st)
+
 	data := &nodeData{
 		ID:               st.Self.ID,
 		Status:           st.BackendState,
 		DeviceName:       strings.Split(st.Self.DNSName, ".")[0],
+		IPv4:             ipv4,
+		IPv6:             ipv6,
 		OS:               st.Self.OS,
 		IPNVersion:       strings.Split(st.Version, "-")[0],
 		Profile:          st.User[st.Self.UserID],
@@ -887,10 +891,6 @@ func (s *Server) serveGetNodeData(w http.ResponseWriter, r *http.Request) {
 		ACLAllowsAnyIncomingTraffic: s.aclsAllowAccess(filterRules),
 	}
 
-	ipv4, ipv6 := s.selfNodeAddresses(r, st)
-	data.IPv4 = ipv4.String()
-	data.IPv6 = ipv6.String()
-
 	if hostinfo.GetEnvType() == hostinfo.HomeAssistantAddOn && data.URLPrefix == "" {
 		// X-Ingress-Path is the path prefix in use for Home Assistant
 		// https://developers.home-assistant.io/docs/add-ons/presentation#ingress