Allow all interfaces in SQM's interface name dropdown menu

The old implementation presented all real interfaces currently in up state.
Unfortunatelly this does not show PPPoE interfaces, but for PPPoE lines
the packet classification currently only works if pppoe-$DEV (with e.g. DEV=ge00).
The new imlplementation was inspired by luci-app-wol and presents
everything including ifb, while potentially confusing it at least allows proper
traffic shaping on pppoe managed connections.