NFSD: handle errors better in write_ports_addfd()

If write_ports_add() fails, we shouldn't destroy the serv, unless we had
only just created it.  So if there are any permanent sockets already
attached, leave the serv in place.
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfsctl.c

@@ -742,7 +742,7 @@ static ssize_t __write_ports_addfd(char *buf, struct net *net, const struct cred
 		return err;
 
 	err = svc_addsock(nn->nfsd_serv, fd, buf, SIMPLE_TRANSACTION_LIMIT, cred);
-	if (err < 0) {
+	if (err < 0 && list_empty(&nn->nfsd_serv->sv_permsocks)) {
 		nfsd_destroy(net);
 		return err;
 	}