skbuff: fix error handling in pskb_copy()

There are two problems:
1) "n" was allocated with alloc_skb() so we should free it with
   kfree_skb() instead of regular kfree().
2) We return the freed pointer instead of NULL.
Signed-off-by: Dan Carpenter <error27@gmail.com>
Reviewed-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/skbuff.c

@@ -799,7 +799,8 @@ struct sk_buff *pskb_copy(struct sk_buff *skb, gfp_t gfp_mask)
 
 		if (skb_shinfo(skb)->tx_flags & SKBTX_DEV_ZEROCOPY) {
 			if (skb_copy_ubufs(skb, gfp_mask)) {
-				kfree(n);
+				kfree_skb(n);
+				n = NULL;
 				goto out;
 			}
 			skb_shinfo(skb)->tx_flags &= ~SKBTX_DEV_ZEROCOPY;