A routed subnet-to-subnet tunnel using xfrmi interface systemd-networkd

this test NEED systemd-networkd and not likely to run in a simple namespace.
It could run under docker/podman (with systemd).

Systemd got this feature in commit
f392c065662 ("Merge pull request #12863 from 1848/if_xfrm")
    Added support for xfrm interfaces

https://github.com/systemd/systemd/pull/12863
F32 systemd has xfrmi suspport

Note: if this test is aborted before completion, it leaves the file
/etc/systemd/network/ipsec2.netdev on the host. This cannot be fixed
in time for systemd to read it. Re-running this test then will clean
this up and the run after that can then be used as proper test case.

