Attempts to force ipv4 for local ifaces

As described in jakobadam#23, there are several options available to force an
ipv4 connection for the guest. Otherwise, the built box comes up with an
unroutable ipv6 address that can't get out.

So far, none of these options have resolved the issue.

debian/debian9-vagrant.json

@@ -45,6 +45,10 @@
                    "passwd/username={{user `user`}} ",
 
                    "<enter>"
+            ],
+            "qemuargs": [
+                [ "-netdev", "user,hostfwd=tcp::{{ .SSHHostPort }}-:22,id=user.0,ipv4"],
+                [ "-device", "virtio-net,netdev=user.0"]
             ]
         }
     ],

debian/http/preseed.cfg

@@ -18,8 +18,12 @@ d-i partman/confirm_nooverwrite boolean true
 d-i partman/confirm_write_new_label boolean true
 d-i partman/default_filesystem string ext4
 d-i passwd/root-login boolean false
-d-i pkgsel/include string openssh-server aptitude
+d-i pkgsel/include string openssh-server aptitude resolvconf
 d-i pkgsel/upgrade select full-upgrade
 d-i time/zone string CET
+d-i preseed/late_command string \
+    if [ -x "/target/sbin/rdnssd" -a ! -x "/target/sbin/resolvconf" ] ; then \
+        in-target systemctl disable rdnssd.service ; \
+    fi
 popularity-contest popularity-contest/participate boolean false
 tasksel tasksel/first multiselect standard