use iptables-restore in all ikev2 firewall scenarios

testing/tests/ikev2/dhcp-dynamic/posttest.dat

@@ -3,8 +3,8 @@ carol::ipsec stop
 dave::ipsec stop
 venus::cat /var/state/dhcp/dhcpd.leases
 venus::/etc/init.d/isc-dhcp-server stop 2> /dev/null
-moon::/etc/init.d/iptables stop 2> /dev/null
-carol::/etc/init.d/iptables stop 2> /dev/null
-dave::/etc/init.d/iptables stop 2> /dev/null
+moon::iptables-restore < /etc/iptables.flush
+carol::iptables-restore < /etc/iptables.flush
+dave::iptables-restore < /etc/iptables.flush
 alice::arp -d 10.1.0.50
 alice::arp -d 10.1.0.51