types/netmap: start phasing out Addresses, add GetAddresses method

NetworkMap.Addresses is redundant with the SelfNode.Addresses. This
works towards a TODO to delete NetworkMap.Addresses and replace it
with a method.

This is similar to #9389.

Updates #cleanup

Change-Id: Id000509ca5d16bb636401763d41bdb5f38513ba0
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

ipn/ipnlocal/serve.go

@@ -205,7 +205,9 @@ func (b *LocalBackend) updateServeTCPPortNetMapAddrListenersLocked(ports []uint1
 		return
 	}
 
-	for _, a := range nm.Addresses {
+	addrs := nm.GetAddresses()
+	for i := range addrs.LenIter() {
+		a := addrs.At(i)
 		for _, p := range ports {
 			addrPort := netip.AddrPortFrom(a.Addr(), p)
 			if _, ok := b.serveListeners[addrPort]; ok {