rtw88: add dynamic rrsr configuration

Register rrsr determines the response rate we send.
In field tests, using rate higher than current tx rate could lead
to difficulty for the receiving end to receive management/control
frames. Calculate current modulation level by tx rate then cross out
rate higher than those.

Signed-off-by: Po-Hao Huang <phhuang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210209070755.23019-2-pkshih@realtek.com