wil6210: RX high threshold interrupt configuration

Rx high threshold interrupt is reported by the hardware in case
when number of not utilized by the HW descriptors in the Rx ring
becomes low.
Introduce module parameter for RX high threshold.

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