policy/v2: let autogroup:internet rules lift via exit steering

A regular rule to the internet allows every exit node, but
autogroup:internet resolves to no prefix, so it never matched.

Updates #3493

hscontrol/policy/v2/issue_3233_test.go

@@ -161,6 +161,11 @@ func TestViaInternetExitSteeringSurvivesUnrelatedRules(t *testing.T) {
 			extra:        `"acls": [{"action": "accept", "src": ["autogroup:member"], "dst": ["tag:exit-b:*"]}],`,
 			wantExcluded: true,
 		},
+		{
+			name:         "acl-autogroup-internet",
+			extra:        `"acls": [{"action": "accept", "src": ["autogroup:member"], "dst": ["autogroup:internet:*"]}],`,
+			wantExcluded: false,
+		},
 		{
 			name:         "acl-wildcard",
 			extra:        `"acls": [{"action": "accept", "src": ["autogroup:member"], "dst": ["*:*"]}],`,

hscontrol/policy/v2/policy.go

@@ -1437,10 +1437,14 @@ func (pm *PolicyManager) ViaRoutesForPeer(viewer, peer types.NodeView) types.Via
 }
 
 // grantReachesInternet reports whether a grant's destinations include
-// the internet. The wildcard resolves to tailnet ranges only, but in a
+// the internet. Neither the wildcard nor autogroup:internet resolves
-// destination it also covers the internet.
+// to 0.0.0.0/0, so check the aliases themselves.
 func grantReachesInternet(grant Grant) bool {
 	return slices.ContainsFunc(grant.Destinations, func(d Alias) bool {
+		if ag, ok := d.(*AutoGroup); ok {
+			return ag.Is(AutoGroupInternet)
+		}
+
 		_, ok := d.(Asterix)
 
 		return ok