link_test.sh

#!/bin/sh

setif() {
  iw dev | grep -q "Interface $1"
  local status=$?
  [ "$2" = "down" ] && [ "$status" = "0" ] && {
    [ -d "/sys/class/net/$1/master" ] && ip link set dev "$1" nomaster
    iw dev "$1" del
    return
  }
  [ "$2" = "up" ] && [ "$status" = "1" ] && {
    wifi
    action=
    return 
  }
}

while true; do

  sleep 30

  action=
  [ "`ip ro sh ta 92 | wc -l`" = "1" ] && action=up || action=down

  for _iface in `uci -q show wireless | grep "wifi-iface$"`; do
    [ "`uci -q get ${_iface%=*}.needuplink`" = "1" ] && setif "`uci -q get ${_iface%=*}.ifname`" $action
  done

done