Fix ifquery call in dhcp-all-interfaces

Ifquery does not print anything for interfaces which only have a single
iface line. It does, however, return non-zero if the interface is not
configured at all, so we can use that to indicate whether or not there
is a configuration.

Fixes bug #1233579

Change-Id: Ia2fdafbea57e806eba99ae8ddaf395ebdcc306e1

elements/dhcp-all-interfaces/install.d/generate-interfaces-file.sh

@@ -12,8 +12,9 @@ function get_if_link() {
 
 for interface in $(ls /sys/class/net | grep -v ^lo$) ; do
   echo -n "Inspecting interface: $interface..."
-  HAS_CONFIG=$(ifquery $interface >/dev/null 2>&1)
-  if [ "$HAS_CONFIG" == "" ]; then
+  if ifquery $interface >/dev/null 2>&1 ; then
+    echo "Has config, skipping."
+  else
     ip link set dev $interface up >/dev/null 2>&1
     HAS_LINK="$(get_if_link $interface)"