use iptables-restore in all ikev2 firewall scenarios

testing/tests/ikev2/nat-rw/posttest.dat

@@ -1,8 +1,8 @@
 sun::ipsec stop
 alice::ipsec stop
 venus::ipsec stop
-alice::/etc/init.d/iptables stop 2> /dev/null
-venus::/etc/init.d/iptables stop 2> /dev/null
-sun::/etc/init.d/iptables stop 2> /dev/null
+alice::iptables-restore < /etc/iptables.flush
+venus::iptables-restore < /etc/iptables.flush
+sun::iptables-restore < /etc/iptables.flush
 moon::iptables -t nat -F
 moon::conntrack -F