wireguard/babel: remove wireguard interface to babeld on the fly

wireguard/files/babel-interfaces-wireguard.j2

@@ -7,6 +7,7 @@ iface {{ iface_prefix }}_{{ peer.name }} inet6 static
     pre-up wg setconf $IFACE /etc/wg/$IFACE.conf
     address fe80::1/64
     post-up echo "interface $IFACE type tunnel link-quality true update-interval 300" | nc ::1 33123
+    post-down echo "flush interface $IFACE" | nc ::1 33123
     post-down ip link del dev $IFACE
 
 {% endfor %}