xen-netback: correct success/error reporting for the SKB-with-fraglist case

When re-entering the main loop of xenvif_tx_check_gop() a 2nd time, the
special considerations for the head of the SKB no longer apply. Don't
mistakenly report ERROR to the frontend for the first entry in the list,
even if - from all I can tell - this shouldn't matter much as the overall
transmit will need to be considered failed anyway.
Signed-off-by: NJan Beulich <jbeulich@suse.com>
Reviewed-by: NPaul Durrant <paul@xen.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/xen-netback/netback.c

@@ -499,7 +499,7 @@ static int xenvif_tx_check_gop(struct xenvif_queue *queue,
 				 * the header's copy failed, and they are
 				 * sharing a slot, send an error
 				 */
-				if (i == 0 && sharedslot)
+				if (i == 0 && !first_shinfo && sharedslot)
 					xenvif_idx_release(queue, pending_idx,
 							   XEN_NETIF_RSP_ERROR);
 				else