bmips: add experimental ethernet support

This adds experimental ethernet support for BCM6318, BCM6328, BCM6362, BCM6368
and BCM63268.
BCM6358 needs a different driver, so there's no support for now.

Working devices:
- Comtrend AR-5315u
- Comtrend AR-5387un
- Comtrend VR-3025u
- Comtrend VR-3032u

Not working devices:
- Netgear DGND3700 v2 (no idea on how the external switch is connected)
- Huawei HG556a ver B (BCM6358 needs a separate driveer)

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>

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

@@ -0,0 +1,15 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+. /lib/functions/uci-defaults.sh
+
+board_config_update
+
+case "$(board_name)" in
+comtrend,vr-3032u)
+	ucidef_set_interface_lan "lan1 lan2 lan3 lan4"
+	;;
+esac
+
+board_config_flush
+
+exit 0