hardware offloading: resolve bridge interfaces

common/linux_iphelper.sh

@@ -109,3 +109,20 @@ unprepare_route_localnet()
 {
 	set_route_localnet 0 "$@"
 }
+
+resolve_lower_devices()
+{
+	# $1 - bridge interface name
+	[ -d "/sys/class/net/$1" ] && {
+		find "/sys/class/net/$1" -follow -maxdepth 1 -name "lower_*" |
+		{
+			local l lower lowers
+			while read lower; do
+				lower=$(basename "$lower")
+				l="${lower#lower_*}"
+				[  "$l" != "$lower" ] && append_separator_list lowers ' ' '' "$l"
+			done
+			printf "$lowers"
+		}
+	}
+}