Nat to nat (#146)

* wireguard: export an Endpoint comparison method

* Record discovered endpoints in node

* Synchronize DiscoveredEndpoints in k8s backend

* Add discoveredEndpointsAreEqual

* Handle discovered Endpoints in topology to enable NAT 2 NAT

* Refactor to use Endpoint.Equal

Compare IP first by default and compare DNS name first when we know the Endpoint was resolved.

* Drop the shallow copies of nodes and peers

Now that updateNATEndpoints was updated to discoverNATEndpoints and that
the endpoints are overridden by topology instead of mutating the nodes and
peers object, we can safely drop this copy.

pkg/mesh/backend.go

@@ -66,6 +66,7 @@ type Node struct {
 	PersistentKeepalive int
 	Subnet              *net.IPNet
 	WireGuardIP         *net.IPNet
+	DiscoveredEndpoints map[string]*wireguard.Endpoint
 }
 
 // Ready indicates whether or not the node is ready.