AioContext: take bottom halves into account when computing aio_poll timeout

Right now, QEMU invokes aio_bh_poll before the "poll" phase
of aio_poll.  It is simpler to do it afterwards and skip the
"poll" phase altogether when the OS-dependent parts of AioContext
are invoked from GSource.  This way, AioContext behaves more
similarly when used as a GSource vs. when used as stand-alone.

As a start, take bottom halves into account when computing the
poll timeout.  If a bottom half is ready, do a non-blocking
poll.  As a side effect, this makes idle bottom halves work
with aio_poll; an improvement, but not really an important
one since they are deprecated.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
diff --git a/aio-win32.c b/aio-win32.c
index c12f61e..fe7ee5b 100644
--- a/aio-win32.c
+++ b/aio-win32.c
@@ -165,8 +165,8 @@
     while (count > 0) {
         int ret;
 
-        timeout = blocking ?
-            qemu_timeout_ns_to_ms(timerlistgroup_deadline_ns(&ctx->tlg)) : 0;
+        timeout = blocking
+            ? qemu_timeout_ns_to_ms(aio_compute_timeout(ctx)) : 0;
         ret = WaitForMultipleObjects(count, events, FALSE, timeout);
 
         /* if we have any signaled events, dispatch event */