wifi: mac80211: use RCU-safe iteration in ieee80211_csa_finish

wifi: mac80211: use RCU-safe iteration in ieee80211_csa_finish

The ieee80211_csa_finish() function currently uses for_each_sdata_link()
to iterate over links of sdata. However, this macro internally uses
wiphy_dereference(), which expects the wiphy->mtx lock to be held.
When ieee80211_csa_finish() is invoked under an RCU read-side critical
section (e.g., under rcu_read_lock()), this leads to a warning from the
RCU debugging framework.

  WARNING: suspicious RCU usage
  net/mac80211/cfg.c:3830 suspicious rcu_dereference_protected() usage!

This warning is triggered because wiphy_dereference() is not safe to use
without holding the wiphy mutex, and it is being used in an RCU context
without the required locking.

Fix this by introducing and using a new macro, for_each_sdata_link_rcu(),
which performs RCU-safe iteration over sdata links using
list_for_each_entry_rcu() and rcu_dereference(). This ensures that the
link pointers are accessed safely under RCU and eliminates the warning.

Fixes: f600832794c9 ("wifi: mac80211: restructure tx profile retrieval for MLO MBSSID")
Signed-off-by: Maharaja Kennadyrajan <maharaja.kennadyrajan@oss.qualcomm.com>
Link: https://patch.msgid.link/20250711033846.40455-1-maharaja.kennadyrajan@oss.qualcomm.com
[unindent like the non-RCU macro]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>