Commit 2e2aa316 removed internal flag msi_in_use, but it
existed in vmstate. Restore it for migration to older QEMU
versions.
Reported-by: Amit Shah <amit.shah@redhat.com>
Suggested-by: Amit Shah <amit.shah@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>
Cc: Marcel Apfelbaum <marcel@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Amit Shah <amit.shah@redhat.com>
Cc: Cao jin <caoj.fnst@cn.fujitsu.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>