skbuff/mac80211: introduce and use skb_put_zero()

This pattern was introduced a number of times in mac80211 just now,
and since it's present in a number of other places it makes sense
to add a little helper for it.

This just adds the helper and transforms the mac80211 code, a later
patch will transform other places.

Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/mesh_plink.c

@@ -264,8 +264,7 @@ static int mesh_plink_frame_tx(struct ieee80211_sub_if_data *sdata,
 		band = sband->band;
 
 		/* capability info */
-		pos = skb_put(skb, 2);
-		memset(pos, 0, 2);
+		pos = skb_put_zero(skb, 2);
 		if (action == WLAN_SP_MESH_PEERING_CONFIRM) {
 			/* AID */
 			pos = skb_put(skb, 2);