End grace for the NFSv4 server if all mounts do ReclaimComplete.

The NFSv4 protocol requires that the server only allow reclaim of state
and not issue any new open/lock state for a grace period after booting.
The NFSv4.0 protocol required this grace period to be greater than the
lease duration (over 2minutes). For NFSv4.1, the client tells the server
that it has done reclaiming state by doing a ReclaimComplete operation.
If all NFSv4 clients are NFSv4.1, the grace period can end once all the
clients have done ReclaimComplete, shortening the time period considerably.
This patch does this. If there are any NFSv4.0 mounts, the grace period
will still be over 2minutes.
This change is only an optimization and does not affect correct operation.

Tested by: andreas.nagy@frequentis.com
MFC after: 2 months