wifi: rtw89: mac: set NAV upper to 25ms

NAV upper register is to limit the maximum NAV value to prevent
unexpected NAV, but the old setting is too small to reflect NAV from
AP transmiting big MPDU at once.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220916033811.13862-3-pkshih@realtek.com