Another round of Kobo Fixes (#3939)

* Trim unneeded stuff from startup script

I was somehow convinced I'd already done that...
While we're there, explain why we need to siphon those specific vars

* Fix a stray eth0

-> $INTERFACE

* Be very very sure we have INTERFACE set in our env

re #3936

* Make getFirmwareVersion less fragile on Kobo

Not that we actually use it right now, but, still. :D

* Use the same syntax as the PRODUCT check

* Actually implement getProductId

Instead of a stray c/p ^^

* Properly identify the Rev2/Mark7 variants of existing devices

Namely, the H2O² and Aura SE
Not that the H2O²r2 support is still broken, this just allows us to
implement it cleanyl without breaking handling of the original H2O²

re #3925

* Tweak sleeps a bit around Kobo WiFi modules...

See if that jog things up (re #3936)

* Try harder not to suspend with WiFi on on Kobos

Because otherwise, things go boom. (re #3936)

frontend/device/generic/device.lua

@@ -142,7 +142,12 @@ function Device:onPowerEvent(ev)
         self.screen_saver_mode = true
         UIManager:scheduleIn(0.1, function()
           local network_manager = require("ui/network/manager")
-          if network_manager.wifi_was_on then
+          -- NOTE: wifi_was_on does not necessarily mean that WiFi is *currently* on! It means *we* enabled it.
+          --       This is critical on Kobos (c.f., #3936), where it might still be on from KSM or Nickel,
+          --       without us being aware of it (i.e., wifi_was_on still unset or false),
+          --       because suspend will at best fail, and at worst deadlock the system if WiFi is on,
+          --       regardless of who enabled it!
+          if network_manager.wifi_was_on or network_manager:isWifiOn() then
               network_manager:releaseIP()
               network_manager:turnOffWifi()
           end