Revert "openwrt: use less-ambigouus variable to determine just-added"

This reverts commit 8c1c35271ddf08c8bf5051b2df71d08a16a1c67d.
Revert "openwrt: avoid some more ubus/netifd-induced race-conditions"

This reverts commit 0dcfd55e376a8bfaa5170e508e73eba259126231.
openwrt: react immediately on interface down