nfsd4: make sure sequence flags are set after destroy_session

If this loses any backchannel, make sure we have a chance to notice that
and set the sequence flags.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>
diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
index 32ff615..4e5bdfd 100644
--- a/fs/nfsd/state.h
+++ b/fs/nfsd/state.h
@@ -464,6 +464,7 @@
 extern void nfs4_free_stateowner(struct kref *kref);
 extern int set_callback_cred(void);
 extern void nfsd4_probe_callback(struct nfs4_client *clp);
+extern void nfsd4_probe_callback_sync(struct nfs4_client *clp);
 extern void nfsd4_change_callback(struct nfs4_client *clp, struct nfs4_cb_conn *);
 extern void nfsd4_do_callback_rpc(struct work_struct *);
 extern void nfsd4_cb_recall(struct nfs4_delegation *dp);