at86rf230: move cal_timeout to state change

This patch moves the calculation timeout of TRX_OFF to RX_AACK_ON
handling to the async state change functionality. With this patch we can
do a reset of calculation timeout when others TRX_OFF to RX_AACK_ON
happens instead of doing this on interface up only.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Reviewed-by: Varka Bhadram <varkabhadram@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>