The unified keventd has no automated coverage, only the devmon
fallback is exercised by the test suite. Network interfaces are
the one device class an unprivileged test can hotplug: the sandbox
has its own network namespace, so 'ip link add' makes the kernel
emit genuine uevents.
Verify keventd readiness, <class/net/IFNAME> driving a service --
and <dev/IFNAME> NOT asserted, interfaces are not device nodes --
libudev-compatible n<ifindex> keying in /run/udev/data, conditions
surviving initctl reload, and cleanup on interface remove.
Signed-off-by: Joachim Wiberg <troglobit@gmail.com>