add migration state change notifiers

This patch adds functions to register and unregister notifiers for
migration state changes and a function to query the migration state.
The notifier is called on every state change.  Once after establishing a
new migration object (which is in active state then) and once when the
state changes from active to completed, canceled or error.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
diff --git a/migration.h b/migration.h
index d13ed4f..21707922 100644
--- a/migration.h
+++ b/migration.h
@@ -16,6 +16,7 @@
 
 #include "qdict.h"
 #include "qemu-common.h"
+#include "notify.h"
 
 #define MIG_STATE_ERROR		-1
 #define MIG_STATE_COMPLETED	0
@@ -134,4 +135,8 @@
     return container_of(mig_state, FdMigrationState, mig_state);
 }
 
+void add_migration_state_change_notifier(Notifier *notify);
+void remove_migration_state_change_notifier(Notifier *notify);
+int get_migration_state(void);
+
 #endif