testing: Add ikev2/net2net-iptfs scenario

testing/tests/ikev2/net2net-iptfs/description.txt

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+A connection between the subnets behind the gateways <b>moon</b> and <b>sun</b> is set up
+enabling IP-TFS (RFC 9347) to aggregate small packets into a single ESP packets and
+fragment large packets across multiple ESP packets.
+The authentication is based on <b>X.509 certificates</b>.
+<p/>
+Upon the successful establishment of the IPsec tunnel, the updown script automatically
+inserts iptables-based firewall rules that let pass the tunneled traffic.
+In order to test both tunnel and firewall, client <b>alice</b> behind gateway <b>moon</b>
+sends several pings to client <b>bob</b> located behind gateway <b>sun</b>.