gluon-radvd: Use procd in init script

The main advantage is that procd is capable of logging stderr to logd,
making errors easier to debug.

package/gluon-radvd/files/etc/init.d/gluon-radvd

 #!/bin/sh /etc/rc.common
 
+USE_PROCD=1
 START=50
 
-SERVICE_WRITE_PID=1
-SERVICE_DAEMONIZE=1
-
-
-start() {
+start_service() {
   [ -x /lib/gluon/radvd/arguments ] && {
-	service_start /usr/sbin/uradvd $(/lib/gluon/radvd/arguments)
+    procd_open_instance
+    procd_param command /usr/sbin/uradvd $(/lib/gluon/radvd/arguments)
+    procd_set_param respawn ${respawn_threshold:-3600} ${respawn_timeout:-5} ${respawn_retry:-5}
+    procd_set_param netdev br-client
+    procd_set_param stderr 1
+    procd_close_instance
   }
 }
-
-stop() {
-	service_stop /usr/sbin/uradvd
-}