realtek: Avoid empty lan mac in initial network setup

If the lan_mac cannot be found, it is still used (as empty string) in
various operations. This is not valid and other 02_network scripts checking
for a non-empty string before using it. This should also be adopted for the
realtek 02_network.

Signed-off-by: Sven Eckelmann <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/20241
Signed-off-by: Hauke Mehrtens <[email protected]>

target/linux/realtek/base-files/etc/board.d/02_network

@@ -97,11 +97,11 @@ realtek_setup_macs()
 		;;
 	esac
 
-	ucidef_set_interface_macaddr "lan" $lan_mac
-	ucidef_set_bridge_mac "$lan_mac"
-	ucidef_set_network_device_mac eth0 $lan_mac
+	[ -n "$lan_mac" ] && ucidef_set_interface_macaddr "lan" $lan_mac
+	[ -n "$lan_mac" ] && ucidef_set_bridge_mac "$lan_mac"
+	[ -n "$lan_mac" ] && ucidef_set_network_device_mac eth0 $lan_mac
 
-	[ -z "$lan_mac_start" ] && lan_mac_start=$lan_mac
+	[ -z "$lan_mac_start" -a -n "$lan_mac" ] && lan_mac_start=$lan_mac
 	realtek_setup_macs_lan "$lan_list" "$lan_mac_start" "$lan_mac_end"
 
 	[ -n "$label_mac" ] && ucidef_set_label_macaddr $label_mac