all: use iterators over slice views more

This gets close to all of the remaining ones.

Updates #12912

Change-Id: I9c672bbed2654a6c5cab31e0cbece6c107d8c6fa
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

ipn/ipnlocal/serve.go

@@ -242,8 +242,7 @@ func (b *LocalBackend) updateServeTCPPortNetMapAddrListenersLocked(ports []uint1
 	}
 
 	addrs := nm.GetAddresses()
-	for i := range addrs.Len() {
-		a := addrs.At(i)
+	for _, a := range addrs.All() {
 		for _, p := range ports {
 			addrPort := netip.AddrPortFrom(a.Addr(), p)
 			if _, ok := b.serveListeners[addrPort]; ok {