added new scenarios

testing/tests/ikev2/double-nat-net/description.txt

@@ -0,0 +1,7 @@
+The roadwarrior <b>alice</b> sitting behind the NAT router <b>moon</b> sets up a
+tunnel to the subnet hiding behind the NAT router <b>sun</b>. All IKE and ESP traffic
+directed to the router <b>sun</b> is forwarded to the VPN gateway <b>bob</b>
+using destination NAT.  UDP encapsulation is used to traverse the NAT routers.
+<b>leftfirewall=yes</b> automatically inserts iptables-based firewall rules that
+let pass the tunneled traffic. In order to test the double NAT-ed IPsec
+tunnel <b>alice</b> pings the inner IP address of the router <b>sun</b>.