rt2800: use RTS/CTS protection instead of CTS-to-self

Change default to RTS/CTS protection. This has a cost of transmitting
one more control frame (RTS) however protect us from traffic from
hidden node.

On station mode will use CTS-to-self if AP will configure that
for the network.

Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>