net: limit scope of a skb_zerocopy_iter_stream var

skb_zerocopy_iter_stream() only uses @orig_uarg in the !link_skb path,
and we can move the local variable in the appropriate block.
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

@@ -1871,7 +1871,6 @@ int skb_zerocopy_iter_stream(struct sock *sk, struct sk_buff *skb,
 			     struct msghdr *msg, int len,
 			     struct ubuf_info *uarg)
 {
-	struct ubuf_info *orig_uarg = skb_zcopy(skb);
 	int err, orig_len = skb->len;
 
 	if (uarg->ops->link_skb) {
@@ -1879,6 +1878,8 @@ int skb_zerocopy_iter_stream(struct sock *sk, struct sk_buff *skb,
 		if (err)
 			return err;
 	} else {
+		struct ubuf_info *orig_uarg = skb_zcopy(skb);
+
 		/* An skb can only point to one uarg. This edge case happens
 		 * when TCP appends to an skb, but zerocopy_realloc triggered
 		 * a new alloc.