ar71xx: wndr4300: change 'orange' to 'amber' in LED color names

The hardware manual says amber so change the color part of
the LED names to reflect that. Also update the constant names.

Based on the the WNDR3700v4 support patch from Ralph Perlich:
  http://patchwork.openwrt.org/patch/4763/



Signed-off-by: Gabor Juhos <juhosg@openwrt.org>

SVN-Revision: 40473