gluon-radvd: remove netdev from initscript

uradvd will tolerate devices appearing and disappearing during runtime.

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

@@ -8,7 +8,6 @@ start_service() {
     procd_open_instance
     procd_set_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
   }