NFSv4.1: new flag for lease time check

Data servers cannot send nfs4_proc_get_lease_time. but still need to setup
state renewal. Add the NFS_CS_CHECK_LEASE_TIME bit to indicate if the lease
time can be checked.

Signed-off-by: Andy Adamson <andros@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>