wifi: rtw89: chan: refine MCC re-plan flow when unassign chanctx

Originally during unassign-chanctx, MCC (multi-channel concurrency) is
re-planed before set-channel if need. But, we might calculate MCC stuffs
based on old channel info. And, the following set-channel might be racing
with FW MCC state mechanism. So, we refine this flow. Now, if MCC re-plan
is needed here, it will be done after set-channel.

Besides, to be more rigorous, we now ensure entity isn't paused before we
deal with MCC things here.

Signed-off-by: Zong-Zhe Yang <kevin_yang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20240727080650.12195-2-pkshih@realtek.com