migration: run setup callbacks out of big lock

Only the migration_bitmap_sync() call needs the iothread lock.

Reviewed-by: Orit Wasserman <owasserm@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
diff --git a/savevm.c b/savevm.c
index e10a045..7c7774e 100644
--- a/savevm.c
+++ b/savevm.c
@@ -1768,7 +1768,10 @@
         return -EINVAL;
     }
 
+    qemu_mutex_unlock_iothread();
     qemu_savevm_state_begin(f, &params);
+    qemu_mutex_lock_iothread();
+
     while (qemu_file_get_error(f) == 0) {
         if (qemu_savevm_state_iterate(f) > 0) {
             break;