ar71xx: don't use D-Link DIR-505 status LED as ethernet indicator

The stock firmware uses the single LED as status indicator only. Using the
same LED both for status and as ethernet indicator is uncommon, and has
been confusing users who were using the device as a WLAN mesh node (so the
LED was just off, as no ethernet was connected).

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