Add the -S flag to mountd.

-S      Tell mountd to suspend/resume execution of the nfsd threads when
        ever the exports list is being reloaded.  This avoids intermit-
        tent access errors for clients that do NFS RPCs while the exports
        are being reloaded, but introduces a delay in RPC response while
        the reload is in progress.  If mountd crashes while an exports
        load is in progress, mountd must be restarted to get the nfsd
        threads running again, if this option is used.

Ticket: #3878