chore: account for resource sorting in dns upstream resource

`List` returns a sorted (by id) list of resources. This doesn't work when the order of dns upstreams is important. Because of that
we need to rework "DNSUpstreams.net.talos.dev" resource ID from destination host to "dns №<num>".

Fixes siderolabs#9274

Signed-off-by: Dmitriy Matrenichev <dmitry.matrenichev@siderolabs.com>

internal/app/machined/pkg/controllers/network/dns_upstream.go

@@ -6,6 +6,7 @@ package network
 
 import (
 	"context"
+	"fmt"
 	"net"
 	"time"
 
@@ -103,17 +104,25 @@ func (ctrl *DNSUpstreamController) run(ctx context.Context, r controller.Runtime
 		return err
 	}
 
-	for _, s := range rs.TypedSpec().DNSServers {
+	for i, s := range rs.TypedSpec().DNSServers {
 		remoteAddr := s.String()
 
 		if err = safe.WriterModify[*network.DNSUpstream](
 			ctx,
 			r,
-			network.NewDNSUpstream(remoteAddr),
+			network.NewDNSUpstream(fmt.Sprintf("dns upstream №%d", i+1)),
 			func(u *network.DNSUpstream) error {
 				touchedIDs[u.Metadata().ID()] = struct{}{}
 
 				if u.TypedSpec().Value.Prx != nil {
+					if u.TypedSpec().Value.Prx.Addr() == net.JoinHostPort(remoteAddr, "53") {
+						// existing upstream in this position is already correct
+						return nil
+					}
+
+					// existing upstream in this position is incorrect, stop it
+					u.TypedSpec().Value.Prx.Stop()
+
 					return nil
 				}
 

internal/app/machined/pkg/controllers/network/resolver_merge.go

@@ -94,9 +94,7 @@ func (ctrl *ResolverMergeController) Run(ctx context.Context, r controller.Runti
 		}
 
 		if final.DNSServers != nil {
-			if err = r.Modify(ctx, network.NewResolverSpec(network.NamespaceName, network.ResolverID), func(res resource.Resource) error {
-				spec := res.(*network.ResolverSpec) //nolint:errcheck,forcetypeassert
-
+			if err = safe.WriterModify(ctx, r, network.NewResolverSpec(network.NamespaceName, network.ResolverID), func(spec *network.ResolverSpec) error {
 				*spec.TypedSpec() = final
 
 				return nil
@@ -150,9 +148,9 @@ func mergeDNSServers(dst *[]netip.Addr, src []netip.Addr) {
 	// and same vice versa for IPv6
 	switch {
 	case dstHasV4 && !srcHasV4:
-		*dst = append(slices.Clone(src), filterIPFamily(*dst, true)...)
+		*dst = slices.Concat(src, filterIPFamily(*dst, true))
 	case dstHasV6 && !srcHasV6:
-		*dst = append(slices.Clone(src), filterIPFamily(*dst, false)...)
+		*dst = slices.Concat(src, filterIPFamily(*dst, false))
 	default:
 		*dst = src
 	}