Switch nsd control socket from localhost to a unix domain socket.

OK sthen

src/etc/nsd.conf

@@ -1,4 +1,4 @@
-# $OpenBSD: nsd.conf,v 1.12 2018/05/18 05:15:33 florian Exp $
+# $OpenBSD: nsd.conf,v 1.13 2018/08/16 17:59:12 florian Exp $
 
 server:
 	hide-version: yes
@@ -19,6 +19,7 @@ server:
 
 remote-control:
 	control-enable: yes
+	control-interface: /var/run/nsd.sock
 
 ## tsig key example
 #key: