Default local listeners to 127.0.0.1

Client TCP/UDP and the built-in DNS server bind loopback unless bind_address or a per-rule host (tcp://22:0.0.0.0:2222) is set. README and generated server examples no longer document :9000/:8080 as if they were localhost-only.

Closes #3

pkg/dns/dns.go

@@ -1,7 +1,6 @@
 package dns
 
 import (
-	"fmt"
 	"net"
 	"strings"
 	"time"
@@ -18,9 +17,10 @@ func StartDNSServer(cfg *config.Config) {
 		return
 	}
 
+	listenAddr := cfg.DNSServer.ListenAddr()
 	// Create DNS server
 	server := &dns.Server{
-		Addr: fmt.Sprintf(":%d", cfg.DNSServer.ListenPort),
+		Addr: listenAddr,
 		Net:  "udp",
 	}
 
@@ -29,7 +29,10 @@ func StartDNSServer(cfg *config.Config) {
 		handleDNSQuery(w, r, cfg)
 	})
 
-	logger.WithField("port", cfg.DNSServer.ListenPort).Info("DNS server started")
+	logger.WithFields(map[string]interface{}{
+		"addr": listenAddr,
+		"port": cfg.DNSServer.ListenPort,
+	}).Info("DNS server started")
 
 	// Start server
 	if err := server.ListenAndServe(); err != nil {