unbound: rework dns-forwader handling

add check if red interface has an IPv4 address before test the servers at
red up and simply remove forwarders at down process.

This also fix the hung at dhcpd shutdown.

Signed-off-by: Arne Fitzenreiter <arne_f@ipfire.org>

src/initscripts/networking/red.down/05-remove-dns-forwarders

@@ -0,0 +1,4 @@
+#!/bin/bash
+
+# Remove DNS forwarders for unbound
+exec /etc/init.d/unbound remove-forwarders

src/initscripts/networking/red.down/05-update-dns-forwarders

@@ -1,4 +0,0 @@
-#!/bin/bash
-
-# Update DNS forwarders for unbound
-exec /etc/init.d/unbound update-forwarders