Treat 0.0.0.0 as local address in --address flag (#4386)

cmd/net.go

@@ -319,7 +319,10 @@ func CheckLocalServerAddr(serverAddr string) error {
 		return fmt.Errorf("port number must be between 1 to 65535")
 	}
 
-	if host != "" {
+	// 0.0.0.0 is a wildcard address and refers to local network
+	// addresses. I.e, 0.0.0.0:9000 like ":9000" refers to port
+	// 9000 on localhost.
+	if host != "" && host != net.IPv4zero.String() {
 		isLocalHost, err := isLocalHost(host)
 		if err != nil {
 			return err

cmd/net_test.go

@@ -221,6 +221,7 @@ func TestCheckLocalServerAddr(t *testing.T) {
 	}{
 		{":54321", nil},
 		{"localhost:54321", nil},
+		{"0.0.0.0:9000", nil},
 		{"", fmt.Errorf("missing port in address")},
 		{"localhost", fmt.Errorf("missing port in address localhost")},
 		{"example.org:54321", fmt.Errorf("host in server address should be this server")},