all: remove LenIter, use Go 1.22 range-over-int instead

Updates #11058
Updates golang/go#65685

Change-Id: Ibb216b346e511d486271ab3d84e4546c521e4e22
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

wgengine/magicsock/debughttp.go

@@ -102,7 +102,7 @@ func (c *Conn) ServeHTTPDebug(w http.ResponseWriter, r *http.Request) {
 		sort.Slice(ent, func(i, j int) bool { return ent[i].pub.Less(ent[j].pub) })
 
 		peers := map[key.NodePublic]tailcfg.NodeView{}
-		for i := range c.peers.LenIter() {
+		for i := range c.peers.Len() {
 			p := c.peers.At(i)
 			peers[p.Key()] = p
 		}

wgengine/magicsock/endpoint.go

@@ -1366,7 +1366,7 @@ func (de *endpoint) updateFromNode(n tailcfg.NodeView, heartbeatDisabled bool, p
 }
 
 func (de *endpoint) setEndpointsLocked(eps interface {
-	LenIter() []struct{}
+	Len() int
 	At(i int) netip.AddrPort
 }) {
 	for _, st := range de.endpointState {
@@ -1374,7 +1374,7 @@ func (de *endpoint) setEndpointsLocked(eps interface {
 	}
 
 	var newIpps []netip.AddrPort
-	for i := range eps.LenIter() {
+	for i := range eps.Len() {
 		if i > math.MaxInt16 {
 			// Seems unlikely.
 			break

wgengine/magicsock/magicsock.go

@@ -1793,7 +1793,7 @@ func nodesEqual(x, y views.Slice[tailcfg.NodeView]) bool {
 	if x.Len() != y.Len() {
 		return false
 	}
-	for i := range x.LenIter() {
+	for i := range x.Len() {
 		if !x.At(i).Equal(y.At(i)) {
 			return false
 		}
@@ -2056,7 +2056,7 @@ func (c *Conn) logEndpointCreated(n tailcfg.NodeView) {
 			fmt.Fprintf(w, "derp=%v%s ", regionID, code)
 		}
 
-		for i := range n.AllowedIPs().LenIter() {
+		for i := range n.AllowedIPs().Len() {
 			a := n.AllowedIPs().At(i)
 			if a.IsSingleIP() {
 				fmt.Fprintf(w, "aip=%v ", a.Addr())
@@ -2064,7 +2064,7 @@ func (c *Conn) logEndpointCreated(n tailcfg.NodeView) {
 				fmt.Fprintf(w, "aip=%v ", a)
 			}
 		}
-		for i := range n.Endpoints().LenIter() {
+		for i := range n.Endpoints().Len() {
 			ep := n.Endpoints().At(i)
 			fmt.Fprintf(w, "ep=%v ", ep)
 		}