wil6210: configurable vring sizes

Allow to configure VRING size for both Rx and Tx via module parameters:
rx_ring_order and tx_ring_order. Parameters are ring size orders, i.e.
ring size calculated as 1 << order.
Defaults for both Tx and Rx are order 9, i.e. size 512

Signed-off-by: Vladimir Kondratiev <qca_vkondrat@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>