This intends to replace the hotplug script. It still hardcodes "wan"
interface name (as several other packages do) for lack of a deterministic
way to detect the actual wan iface before it is brought up, but at least
it is fully integrated with procd and will not start a disabled service.

The interface trigger forcefully restarts chilli as a simple reload may
not be sufficient to recover from wan changes.

Signed-off-by: Thibaut VARÈNE <hacks@slashdirt.org>