wifi: mac80211: make ieee80211_find_chanctx link-unaware

wifi: mac80211: make ieee80211_find_chanctx link-unaware

Currently we have only one user for a channel context: the link.
With NAN, a new type of the channel context user will be added - the NAN
channel.
To prepare for this, we need to separate the channel context code from
the link code.

Removes the link argument from ieee80211_find_chanctx. Since the issue that led
to commit 5e0c422d12b5 ("wifi: mac80211: reserve chanctx during find") - that
added the link argument - is relevant for any user of the channel context, add
a boolean to the chanctx itself, indicating that the chanctx is in the process
of getting used.

When this indication is set, the reference count of the channel context
will be incremented by one, so even if it is getting released from a link
(or another user) it won't be freed.

Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20260320101954.232499e2a41f.I0b735a607e1ec7aa5749ab01c794ef99dbe82b7f@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>