wifi: mac80211: Add link iteration macro for link data

Currently before iterating through valid links we are utilizing
open-coding when checking if vif valid_links is a non-zero value.

Add new macro, for_each_link_data(), which iterates through link_id
and checks if it is set on vif valid_links. If it is a valid link then
access link data for that link id.

Signed-off-by: Muna Sinada <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Johannes Berg <[e-mail]>

net/mac80211/ieee80211_i.h

···
 	if ((_link = wiphy_dereference((_local)->hw.wiphy,		\
 				       ___sdata->link[___link_id])))
 
+#define for_each_link_data(sdata, __link)					\
+	struct ieee80211_sub_if_data *__sdata = sdata;				\
+	for (int __link_id = 0;							\
+	     __link_id < ARRAY_SIZE((__sdata)->link); __link_id++)		\
+		if ((!(__sdata)->vif.valid_links ||				\
+		     (__sdata)->vif.valid_links & BIT(__link_id)) &&		\
+		    ((__link) = sdata_dereference((__sdata)->link[__link_id],	\
+						  (__sdata))))
+
 static inline int
 ieee80211_get_mbssid_beacon_len(struct cfg80211_mbssid_elems *elems,
 				struct cfg80211_rnr_elems *rnr_elems,