ar71xx: Fix WD My Net N600 weak signal issue

ar71xx: Fix WD My Net N600 weak signal issue

The LNAs need to be enabled by setting their respective GPIO to high even
though the original firmware's setting sets them to low on initialization.

Obviously the LNAs are then later initialized by the driver on the OEM
firmware. Without this fix the device is mostly "deaf".

Signed-off-by: Felix Kaechele <heffer@fedoraproject.org>
Tested-by: Steven Haigh <netwiz@crc.id.au>
Patchwork: http://patchwork.openwrt.org/patch/4689/
[juhosg:
  - remove the GPIO LED changes, the My Net N600 has no yellow LEDs at all,
  - change subject and update the commit message]
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@39214 3c298f89-4303-0410-b956-a3cf2f4a3e73