ath9k: Ensure we set FTP_STOMP_LOW weight when WLAN is idle

ath9k: Ensure we set FTP_STOMP_LOW weight when WLAN is idle

When WLAN is idle ensure we downgrade to FTP_STOMP_LOW weight
(from STOMP_LOW) to provide more bandwidth for BT FTP profile.
WLAN's idleness can be estimated by taking into account of the
rx data packets and just ignore beacons, qos nullfunc etc.

Also update bt_wait_time even if the chip is in NETWORK SLEEP
mode. This should help BT throughput when WLAN is idle.

Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>