rsi: Changed the logic of dequeuing packets from hal queues.

The number of packets being dequeued from s/w queues was fixed -
changed it to a dynamic calculation based on txop. There are also
some fixes to the dequeuing algorithm.

Signed-off-by: Jahnavi Meher <jahnavi.meher@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>