rt2x00: Remove rt2x00lib_toggle_rx

As part of the queue refactoring, the rt2x00lib_toggle_rx
can be removed and replaced with the call directly to
the set_device_state callback function.

We can remove the STATE_RADIO_RX_ON_LINK and
STATE_RADIO_RX_OFF_LINK, as it was only used for
special behavior inside rt2x00lib rather then the
drivers.

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