wifi: mac80211: add ieee80211_iter_chan_contexts_mtx

Add a chanctx iterator that can be called from a wiphy-locked context.

Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20250212082137.d85eef3024de.Icda0616416c5fd4b2cbf892bdab2476f26e644ec@changeid


[fix kernel-doc]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>