linux-aio: increasing MAX_EVENTS to a larger hardcoded value

Since commit 6040aedd "virtio-blk:
make queue size configurable",if the user set the queue size to
more than 128 ,it will not take effect. That's because linux aio's
maximum outstanding requests at a time is always less than or equal
to 128.

This patch simply increase MAX_EVENTS to a larger hardcoded value of
1024 as a shortterm fix.
Signed-off-by: Nwangyong <wang.yongD@h3c.com>
Message-id: faa5781afd354a96a0be152b288f636f@h3c.com
Message-Id: <faa5781afd354a96a0be152b288f636f@h3c.com>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

block/linux-aio.c

@@ -26,7 +26,7 @@
  *      than this we will get EAGAIN from io_submit which is communicated to
  *      the guest as an I/O error.
  */
-#define MAX_EVENTS 128
+#define MAX_EVENTS 1024
 
 struct qemu_laiocb {
     Coroutine *co;