mac80211_hwsim: fix-up build damage from removal of skb->dst

Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/mac80211_hwsim.c

@@ -413,8 +413,7 @@ static bool mac80211_hwsim_tx_frame(struct ieee80211_hw *hw,
 
 	/* release the skb's source info */
 	skb_orphan(skb);
-	dst_release(skb->dst);
-	skb->dst = NULL;
+	skb_dst_drop(skb);
 	skb->mark = 0;
 	secpath_reset(skb);
 	nf_reset(skb);