(vagrant) Permanently enable IPv6 on loopback

Required by NSD; The Ubuntu image we use comes with it disabled so we need to
enable it ourselves.

Vagrantfile

@@ -47,6 +47,7 @@ Vagrant.configure("2") do |config|
       m.vm.provision "shell", :inline => <<-SH
         # Make sure we have IPv6 loopback (::1)
         sysctl -w net.ipv6.conf.lo.disable_ipv6=0
+        echo -e "fs.inotify.max_user_instances=1024\nnet.ipv6.conf.lo.disable_ipv6=0" > /etc/sysctl.conf
         # Set environment variables so that the setup script does
         # not ask any questions during provisioning. We'll let the
         # machine figure out its own public IP.