[Net widget] auto-detect new interfaces (Wifi dongles, USB tethering...) within net_update / through another timer

[frenchbeard]

Technical details :

awesome v4.3 (Too long)
 • Compiled against Lua 5.3.6 (running with Lua 5.3)
 • D-Bus support: ✔
 • execinfo support: ✔
 • xcb-randr version: 1.6
 • LGI version: 0.9.2
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lain-git (AUR) : 1:r1786.438dd74-1

Hello, first of all, thanks for the modules, have been using them forever.

I had a question / suggestion on the net widget : as far as I can tell, the net widget currently inits its list of interfaces when Awesome starts, could/should it update it on a given frequency (lower than the rate update, obviously), or should it be left to the "end user" to add a timer that "resets" the widget when a new interface is created ?

Can attempt a PR if this makes sense for the widget.