vagrant: Enable IPv6 and IP forwarding

By default, the most of Vagrant boxes are explicitly disabling IPv6
through sysctl. This change makes sure that IPv6, and also IP forwarding
for all families, are enabled.

This change is necessary for using dual-stack in Vagrant environment.

Signed-off-by: Michal Rostecki <vadorovsky@gmail.com>

scripts/provision/vagrant

@@ -68,6 +68,19 @@ cat <<\EOF >/etc/motd
 
 EOF
 
+# --- Enable IPv6 and IP forwarding
+sysctl -w net.ipv4.ip_forward=1
+sysctl -w net.ipv6.conf.all.disable_ipv6=0
+sysctl -w net.ipv6.conf.all.forwarding=1
+sed -i \
+    -e "/^net.ipv6.conf.all.disable_ipv6 = 1/d" \
+    /etc/sysctl.conf
+cat <<EOF >>/etc/sysctl.conf
+net.ipv4.ip_forward = 1
+net.ipv6.conf.all.disable_ipv6 = 0
+net.ipv6.conf.all.forwarding = 1
+EOF
+
 # --- Utility function to download go
 download_go() {
     goversion=$(grep "golang:" Dockerfile.dapper | sed -e 's/.*golang:\(.*\)-.*/\1/')