ar71xx: WNDR4300: Fix switch HW controlled LEDs

The Netgear WNDR4300, equipped with an Atheros AR8327 Gigabit Switch,
has two LEDs on each port for monitoring LAN activity, but it currently
only uses one. Fix the configuration to use both.

The patch provides this new configuration:
- green LED: 1 Gbps link, 4Hz blink frequency
- amber LED: 10/100 Mbps link. 4Hz for 100Mbps, 2Hz for 10Mbps

Signed-off-by: Daniel Gonzalez Cabanelas <dgcbueu@gmail.com>