ar71xx: fix wndr3700_board_detect for some NETGEAR WNDR3700v2

There are a few NETGEAR devices which don't terminate the model name in the
ART with a NUL byte, at least some NETGEAR WNDR3700v2. The current awk
expression doesn't match 0xFF bytes, so AR71XX_MODEL contains lots of
trailing 0xFF garbage in this case.

Fix this by matching for the first non-printable character and explicitly
setting LC_CTYPE=C (probably not strictly necessary on OpenWrt, but will
definitely work like this, even when awk supports locales and LANG is set).

Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>

Backport of r46455

git-svn-id: svn://svn.openwrt.org/openwrt/branches/chaos_calmer@48087 3c298f89-4303-0410-b956-a3cf2f4a3e73

target/linux/ar71xx/base-files/lib/ar71xx.sh

@@ -38,7 +38,7 @@ wndr3700_board_detect() {
 		;;
 	"33373031")
 		# Use awk to remove everything after the first zero byte
-		model="$(ar71xx_get_mtd_offset_size_format art 41 32 %c | awk 'BEGIN{FS="[[:cntrl:]]"} {print $1; exit}')"
+		model="$(ar71xx_get_mtd_offset_size_format art 41 32 %c | LC_CTYPE=C awk -v 'FS=[^[:print:]]' '{print $1; exit}')"
 		case $model in
 		$'\xff'*)
 			if [ "${model:24:1}" = 'N' ]; then