wifi: rtw89: TX nulldata 0 after scan complete

HW scan leak to TX nulldata 0 to AP after scan completed, which allowed
AP start to TX packet to us. Therefore, driver TX nulldata 0 after scan
completed.

Signed-off-by: Chih-Kang Chang <gary.chang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20250610130034.14692-7-pkshih@realtek.com