[PATCH] rt2x00: Stop link tuning when radio is down

As pointed out by Modestas Vainius the link tuner
could continue working while the radio is already
down. This because at the start of disable_radio
the ENABLED_RADIO flag is cleared and causes the
toggle_rx to skip the stop_link_tuner() call.
This will add a check to the start of the link tuner
which will automatically stop the link tuner when the
radio is disabled.

Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>