bcm63xx: Fast 2704n: configure the WAN port

The Sagem/Plusnet F@ST2704N has a red label in ethernet port 4. Its purpose is
to be used as Fibre/WAN with the stock firmware.

Configure the Eth4 as WAN.

Fixes: fbbb977772 (brcm63xx: Tune the network configuration for several
routers)

Signed-off-by: Daniel González Cabanelas <[email protected]>

target/linux/bcm63xx/base-files/etc/board.d/02_network

@@ -100,8 +100,7 @@ huawei,echolife-hg556a-c)
 	;;
 comtrend,ar-5315u|\
 innacomm,w3400v6|\
-observa,vh4032n|\
-sagem,fast-2704n)
+observa,vh4032n)
 	ucidef_add_switch "switch0" \
 		"0:lan:4" "1:lan:3" "2:lan:2" "3:lan:1" "8t@eth0"
 	;;
@@ -141,6 +140,7 @@ netgear,dgnd3700-v1)
 	ucidef_add_switch "switch0" \
 		"1:lan:4" "2:lan:3" "3:lan:2" "4:lan:1" "0:wan" "8t@eth0"
 	;;
+sagem,fast-2704n|\
 sercomm,ad1018|\
 sercomm,ad1018-nor)
 	ucidef_add_switch "switch0" \