wifi: rtw89: allow driver to do specific band TX for MLO

For data packets that can be sent on any band, fill in main mac_id
and let HW decide. For packets that we wish to transmit on specific
band, fill in sw_mld field so HW would only send it on that band.
Main mac_id is the corresponding mac_id on band 0.

Signed-off-by: Po-Hao Huang <phhuang@realtek.com>
Signed-off-by: Zong-Zhe Yang <kevin_yang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20250505072440.45113-3-pkshih@realtek.com