wifi: cfg80211: use cfg80211_leave() in iftype change

wifi: cfg80211: use cfg80211_leave() in iftype change

When changing the interface type, all activity on the interface has
to be stopped first. This was done independent of existing code in
cfg80211_leave(), so didn't handle e.g. background radar detection.
Use cfg80211_leave() to handle it the same way.

Note that cfg80211_leave() behaves slightly differently for IBSS in
wireless extensions, it won't send an event in that case. We could
handle that, but since nl80211 was used to change the type, IBSS is
rare, and wext is already a corner case, it doesn't seem worth it.

Link: https://patch.msgid.link/20251121174021.922ef48ce007.I970c8514252ef8a864a7fbdab9591b71031dee03@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>