wil6210: allow to configure ADDBA request

For manual ADDBA configuration, allow to set desired window size or
disable automatic mechanism.

Introduce module parameter (int) agg_wsize. It can be changed on run time,
will be taken into account on the next connect. Interpretation:
- <0 - disable automatic ADDBA; intended for manual testing through debugfs
- 0 - use automatically calculated window size
- >0 - use this for window size. Clipped by maximum supported by the hardware
with current environment.

Signed-off-by: Vladimir Kondratiev <qca_vkondrat@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>