gluon-mesh-batman-adv: announce dns server if dns cache was configured (#1105)

package/gluon-mesh-batman-adv/luasrc/lib/gluon/radvd/arguments

@@ -1,3 +1,6 @@
 #!/usr/bin/lua
 local site = require "gluon.site_config"
-print("-i local-node -p " .. site.prefix6)
+io.write("-i local-node -p " .. site.prefix6)
+if site.dns and site.dns.servers then
+	io.write(" --rdnss " .. site.next_node.ip6)
+end