xen-netback: use true and false for boolean values

Return statements in functions returning bool should use true or false
instead of an integer value.

This issue was detected with the help of Coccinelle.
Signed-off-by: NGustavo A. R. Silva <gustavo@embeddedor.com>
Acked-by: NWei Liu <wei.liu2@citrix.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/xen-netback/netback.c

@@ -1603,9 +1603,9 @@ static void xenvif_ctrl_action(struct xenvif *vif)
 static bool xenvif_ctrl_work_todo(struct xenvif *vif)
 {
 	if (likely(RING_HAS_UNCONSUMED_REQUESTS(&vif->ctrl)))
-		return 1;
+		return true;
 
-	return 0;
+	return false;
 }
 
 irqreturn_t xenvif_ctrl_irq_fn(int irq, void *data)