The manager will allow charon-nm to create XFRM interfaces if supported
by the kernel instead of creating an unused dummy TUN interface.
The xfrmi tool is mostly obsolete nowadays as iproute2 supports creating
XFRM interfaces since 5.1.0 (2019-05). Older Debians don't ship that and
early versions didn't list the interface IDs. So there might still be
some uses for this tool.
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?).
