+ clients: find DNS client's hostname by IP using rDNS

dns_test.go

@@ -0,0 +1,9 @@
+package main
+
+import "testing"
+
+func TestResolveRDNS(t *testing.T) {
+	if r := resolveRDNS("1.1.1.1", "1.1.1.1"); r != "one.one.one.one" {
+		t.Errorf("resolveRDNS(): %s", r)
+	}
+}