netifd: fix fw3 warnings in dhcp script

Fix fw3 warnings in dhcp script in case fw3 is not enabled

Signed-off-by: Hans Dedecker <dedeckeh@gmail.com>

package/network/config/netifd/files/lib/netifd/dhcp.script

@@ -60,7 +60,7 @@ setup_interface () {
 		ip6rd="${ip6rd#* }"
 		local ip6rdbr="${ip6rd%% *}"
 
-		[ -n "$ZONE" ] || ZONE=$(fw3 -q network $INTERFACE)
+		[ -n "$ZONE" ] || ZONE=$(fw3 -q network $INTERFACE 2>/dev/null)
 		[ -z "$IFACE6RD" -o "$IFACE6RD" = 1 ] && IFACE6RD=${INTERFACE}_6
 
 		json_init