unbound: add option for dhcp UCI domain mx srv and cname

Base LEDE/OpenWrt UCI for dnsmasq provides for DNS override in
/etc/config/dhcp. It is desired to be able to use dnsmasq and
Unbound as transparently as possible. Option 'add_extra_dns'
will pull 'domain', 'mxhost', 'srvhost, and 'cname' from base.

netifd/procd have an interaction with DHCPv6/RA on WAN (FS#713).
Minor IP6 parameter updates can cause Unbound reload events every
few minutes. List option 'trigger' selects which interfaces may
cause reload. For example 'lan', 'wan' but not 'wan6'.

Squash other cosmetics.

Signed-off-by: Eric Luehrsen <ericluehrsen@hotmail.com>

net/unbound/files/unbound.init

@@ -47,7 +47,7 @@ start_service() {
 
 stop_service() {
   unbound_stop
-  
+
   # Wait! on restart Unbound may take time writing closure stats to syslog
   pidof $PROG && sleep 1
 }
@@ -55,9 +55,20 @@ stop_service() {
 ##############################################################################
 
 service_triggers() {
-  # use soft reload to prevent continuous stop-start and cache flush
+  local trigger
+  local triggers=$( uci_get unbound.@unbound[0].trigger )
+
+  PROCD_RELOAD_DELAY=2000
   procd_add_reload_trigger "unbound"
-  procd_add_raw_trigger "interface.*.up" 2000 /etc/init.d/unbound reload
+
+  if [ -n "$triggers" ] ; then
+    for trigger in $triggers ; do
+      # due to some netifd/procd interactions with IP6, limit interfaces
+      procd_add_reload_interface_trigger "$trigger"
+    done
+  else
+    procd_add_raw_trigger "interface.*.up" 2000 /etc/init.d/unbound reload
+  fi
 }
 
 ##############################################################################