wl1271: Enable hardware keep alive messages

This patch will enable the hardware keep-alive mode, configure the required
template, configure keep-alive parameters, and re-order JOIN's and ACX_AID
in such a way that the keep-alive is activated.

Signed-off-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Reviewed-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>