runtime/race: stop listening to external network addresses

This makes the OS X firewall box pop up.
Not run during all.bash so hasn't been noticed before.

Change-Id: I78feb4fd3e1d3c983ae3419085048831c04de3da
Reviewed-on: https://go-review.googlesource.com/9401Reviewed-by: Austin Clements <austin@google.com>

src/runtime/race/testdata/io_test.go

@@ -49,7 +49,7 @@ func TestNoRaceIOHttp(t *testing.T) {
 			fmt.Fprintf(w, "test")
 			x = 42
 		})
-		err := http.ListenAndServe(":23651", nil)
+		err := http.ListenAndServe("127.0.0.1:23651", nil)
 		if err != nil {
 			t.Fatalf("http.ListenAndServe: %v", err)
 		}