testing: Add ikev2/per-cpu-sas-encap scenario

Basically the same as the one without UDP encapsulation, but here the
outbound SAs use random source ports.

testing/tests/ikev2/per-cpu-sas-encap/posttest.dat

@@ -0,0 +1,5 @@
+moon::swanctl --terminate --ike gw-gw 2> /dev/null
+moon::systemctl stop strongswan
+sun::systemctl stop strongswan
+moon::iptables-restore < /etc/iptables.flush
+sun::iptables-restore < /etc/iptables.flush