testing: Use renamed systemd unit

While the alias is available after enabling the unit, we don't
actually do that in our testing environment (adding a symlink manually
would work too, then again, why not just use the proper name?).

testing/tests/swanctl/net2net-multicast/posttest.dat

@@ -1,3 +1,3 @@
 moon::swanctl --terminate --ike gw-gw 2> /dev/null
-moon::systemctl stop strongswan-swanctl
-sun::systemctl stop strongswan-swanctl
+moon::systemctl stop strongswan
+sun::systemctl stop strongswan

testing/tests/swanctl/net2net-multicast/pretest.dat

@@ -1,7 +1,7 @@
 moon::echo 1 > /proc/sys/net/ipv4/igmp_max_memberships
 sun::echo 1 > /proc/sys/net/ipv4/igmp_max_memberships
-moon::systemctl start strongswan-swanctl
-sun::systemctl start strongswan-swanctl
+moon::systemctl start strongswan
+sun::systemctl start strongswan
 moon::expect-connection gw-gw
 sun::expect-connection gw-gw
 moon::swanctl --initiate --child net-net 2> /dev/null