tools: adapt addpattern for WD's Range Extender

A few things had to be changed to add support for these devices:
 - support code patterns with 8 characters
 - new board definition for the range extender device

Patchwork: http://patchwork.openwrt.org/patch/4280/


Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@38685 3c298f89-4303-0410-b956-a3cf2f4a3e73