AioContext: run bottom halves after polling

Make the dispatching phase the same before blocking and afterwards.
The next patch will make aio_dispatch public and use it directly
for the GSource case, instead of aio_poll.  aio_poll can then be
simplified heavily.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

aio-posix.c

@@ -264,6 +264,10 @@ bool aio_poll(AioContext *ctx, bool blocking)
 
     /* Run dispatch even if there were no readable fds to run timers */
     aio_set_dispatching(ctx, true);
+    if (aio_bh_poll(ctx)) {
+        progress = true;
+    }
+
     if (aio_dispatch(ctx)) {
         progress = true;
     }