TUN inbound: Rename to autoSystemWfpBlockLeak and autoSystemDnsToGateway

autoSystemWFP becomes autoSystemWfpBlockLeak, saying that the WFP filters
block leaks, and autoSystemDNS becomes autoSystemDnsToGateway, saying
where it points the system DNS, so that pointing the system DNS at the
gateway on Windows later would fit the same name. Their config fields
keep their numbers; neither was released.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

proxy/tun/tun_linux_dns_test.go

@@ -58,9 +58,9 @@ func recorder(t *testing.T, failOn string) *[][]string {
 func optedInTun() *LinuxTun {
 	return &LinuxTun{
 		options: &Config{
-			Name:          "xray_tun",
-			Gateway:       []string{"192.168.100.1/30"},
-			AutoSystemDns: true,
+			Name:                   "xray_tun",
+			Gateway:                []string{"192.168.100.1/30"},
+			AutoSystemDnsToGateway: true,
 		},
 		tunLink: testLink("xray_tun"),
 	}
@@ -79,7 +79,7 @@ func TestConfigureSystemDNSDisabledByDefault(t *testing.T) {
 	calls := recorder(t, "")
 
 	t1 := optedInTun()
-	t1.options.AutoSystemDns = false
+	t1.options.AutoSystemDnsToGateway = false
 
 	if err := t1.ConfigureSystemDNS(context.Background(), "tun"); err != nil {
 		t.Fatalf("unexpected error: %v", err)