netback: fix netbk_count_requests()
    
There are two paths in the original code, a) test against work_to_do, b) test
against first->size, could return 0 even when error happens.
    
Simply return -1 in error paths should work. Modify all error paths to return
-1 to be consistent.
    
Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>

Use distinct -E... values instead.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/drivers/xen/netback/netback.c
+++ b/drivers/xen/netback/netback.c
@@ -1042,14 +1042,14 @@ static int netbk_count_requests(netif_t 
 			printk(KERN_ERR "%s: Need more frags\n",
 			       netif->dev->name);
 			netbk_fatal_tx_err(netif);
-			return -frags;
+			return -ENODATA;
 		}
 
 		if (unlikely(frags >= MAX_SKB_FRAGS)) {
 			printk(KERN_ERR "%s: Too many frags\n",
 			       netif->dev->name);
 			netbk_fatal_tx_err(netif);
-			return -frags;
+			return -E2BIG;
 		}
 
 		memcpy(txp, RING_GET_REQUEST(&netif->tx, cons + frags),
@@ -1058,7 +1058,7 @@ static int netbk_count_requests(netif_t 
 			printk(KERN_ERR "%s: Frag is bigger than frame.\n",
 			       netif->dev->name);
 			netbk_fatal_tx_err(netif);
-			return -frags;
+			return -EIO;
 		}
 
 		first->size -= txp->size;
@@ -1068,7 +1068,7 @@ static int netbk_count_requests(netif_t 
 			printk(KERN_ERR "%s: txp->offset: %x, size: %u\n",
 			       netif->dev->name, txp->offset, txp->size);
 			netbk_fatal_tx_err(netif);
-			return -frags;
+			return -EINVAL;
 		}
 	} while ((txp++)->flags & NETTXF_more_data);