wifi: rtw89: chan: move handling from add/remove to assign/unassign for MLO

After MLO, we will need to consider not only active chanctx but also active
interfaces (roles) to decide entity things. So in advance, we move handling
from chanctx_ops::add/remove to chanctx_ops::assign_vif/unassign_vif. Then,
we can recalculate and aware active interfaces' changes.

For now, behavior should not be really different, since active chanctx and
active interface are one-to-one mapping before MLO.

Signed-off-by: Zong-Zhe Yang <kevin_yang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://msgid.link/20240206030624.23382-6-pkshih@realtek.com