net: always try to set ubuf in skb_zerocopy_iter_stream

skb_zcopy_set() does nothing if there is already a ubuf_info associated
with an skb, and since ->link_skb should have set it several lines above
the check here essentially does nothing and can be removed. It's also
safer this way, because even if the callback is faulty we'll
have it set.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

net/core/skbuff.c

@@ -1899,8 +1899,7 @@ int skb_zerocopy_iter_stream(struct sock *sk, struct sk_buff *skb,
 		return err;
 	}
 
-	if (!uarg->ops->link_skb)
-		skb_zcopy_set(skb, uarg, NULL);
+	skb_zcopy_set(skb, uarg, NULL);
 	return skb->len - orig_len;
 }
 EXPORT_SYMBOL_GPL(skb_zerocopy_iter_stream);