Allow the lease to be set from /proc/fs/nfs/nfsv4leasetime.

To comply with rfc3530, this appears as a server reboot from the point of view
of the client, which must reclaim state with the grace period.

From: Andy Adamson <andros@citi.umich.edu>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>