xen/netback: Properly initialize credit_bytes

Commit e9ce7cb6 ("xen-netback: Factor queue-specific data into queue
struct") introduced a regression when moving queue-specific data into
the queue struct by failing to set the credit_bytes field. This
prevented bandwidth limiting from working. Initialize the field as it
was done before multiqueue support was added.
Signed-off-by: NRoss Lagerwall <ross.lagerwall@citrix.com>
Acked-by: NWei Liu <wei.liu2@citrix.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/xen-netback/xenbus.c

@@ -793,6 +793,7 @@ static void connect(struct backend_info *be)
 			goto err;
 		}
 
+		queue->credit_bytes = credit_bytes;
 		queue->remaining_credit = credit_bytes;
 		queue->credit_usec = credit_usec;