ath5k: fix setup for CAB queue

ath5k: fix setup for CAB queue

commit a951ae2176b982574ffa197455db6c89359fd5eb upstream.

The beacon sent gating doesn't seem to work with any combination
of flags.  Thus, buffered frames tend to stay buffered forever,
using up tx descriptors.

Instead, use the DBA gating and hold transmission of the buffered
frames until 80% of the beacon interval has elapsed using the ready
time.  This fixes the following error in AP mode:

   ath5k phy0: no further txbuf available, dropping packet

Add a comment to acknowledge that this isn't the best solution.

Signed-off-by: Bob Copeland <me@bobcopeland.com>
Acked-by: Nick Kossifidis <mickflemm@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>