cfg80211: make wdev_list accessible to drivers

There's no harm in having drivers read the list, since they can
use RCU protection or RTNL locking; allow this to not require
each and every driver to also implement its own bookkeeping.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/net/cfg80211.h

@@ -3189,6 +3189,9 @@ struct wiphy_vendor_command {
  * @vht_capa_mod_mask:  Specify what VHT capabilities can be over-ridden.
  *	If null, then none can be over-ridden.
  *
+ * @wdev_list: the list of associated (virtual) interfaces; this list must
+ *	not be modified by the driver, but can be read with RTNL/RCU protection.
+ *
  * @max_acl_mac_addrs: Maximum number of MAC addresses that the device
  *	supports for ACL.
  *
@@ -3328,6 +3331,8 @@ struct wiphy {
 	const struct ieee80211_ht_cap *ht_capa_mod_mask;
 	const struct ieee80211_vht_cap *vht_capa_mod_mask;
 
+	struct list_head wdev_list;
+
 	/* the network namespace this phy lives in currently */
 	possible_net_t _net;