migration: Switch to using announce timer

Switch the announcements to using the new announce timer.
Move the code that does it to announce.c rather than savevm
because it really has nothing to do with the actual migration.

Migration starts the announce from bh's and so they're all
in the main thread/bql, and so there's never any racing with
the timers themselves.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

migration/migration.h

@@ -21,6 +21,7 @@
 #include "qemu/coroutine_int.h"
 #include "hw/qdev.h"
 #include "io/channel.h"
+#include "net/announce.h"
 
 struct PostcopyBlocktimeContext;
 
@@ -36,6 +37,9 @@ struct MigrationIncomingState {
      */
     QemuEvent main_thread_load_event;
 
+    /* For network announces */
+    AnnounceTimer  announce_timer;
+
     size_t         largest_page_size;
     bool           have_fault_thread;
     QemuThread     fault_thread;