hotplugd - add IFEV_LINK_UP event

[HidingCherry]

I am currently using a custom script to try out MAC pinning on a single port.
For this I have to modify the FDB of the switch.

But - every time the link gets down, the fdb table for this interface is flushed.
There is no hotplugd event when the interface gets back up again, so I have to manually run the script - or write another script for a periodic check.

That's where I found out that there is no hotplugd event for this case.
https://git.openwrt.org/?p=project/netifd.git;a=blob;f=interface-event.c;hb=HEAD#l132

[nvandamme]

It doesn't pass the event to hotplug.d but it does send a ubus event on network.interface.*.
My understanding is that you can listen to ubus event within a shell script with something like:

ubus listen system network.interface.* | while IFS= read -r event; do
    echo "Received event: $event"
    # Add custom logic here (e.g., trigger scripts, log events)
done

https://openwrt.org/docs/techref/ubus#listen