Some devices do not have an address, which prints an error when reading
it.

Signed-off-by: Michael Tremer <michael.tremer(a)ipfire.org>
---
 config/udev/network-hotplug-bridges | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/config/udev/network-hotplug-bridges b/config/udev/network-hotplug-bridges
index bacf722ef..4b8764598 100644
--- a/config/udev/network-hotplug-bridges
+++ b/config/udev/network-hotplug-bridges
@@ -41,9 +41,8 @@ detect_zone() {
 		# Try to find out if this INTERFACE is a slave of a zone
 		local slave
 		for slave in $(get_value "${zone}_SLAVES"); do
-
-			#Compare if the mac address matches or if the name matches
-			if ([ "$(</sys/class/net/${INTERFACE}/address)" = "${slave}" ] || [ "${INTERFACE}" = "${slave}" ]); then
+			# Compare if the mac address matches or if the name matches
+			if [ -r "/sys/class/net/${INTERFACE}/address" -a "$(</sys/class/net/${INTERFACE}/address)" = "${slave}" ] || [ "${INTERFACE}" = "${slave}" ]; then
 				echo "${zone}"
 				return 0
 			fi
-- 
2.30.2