mwifiex: change default tx/rx win_size for BA setup
This patch fixes an issue where RX throughput values observed
were substantially lower than TX counterparts for PCIe8897 STA.
PCIe8897 supports larger rx_win_size. After changing these values
we see big improvement for TX and RX throughput values.
Different tx_win_size and rx_win_size are used for AP mode.
All BA setup related initialization has been moved to separate
function.