NFS4: Fix state renewals missing after boot

Since the last renewal time was initialized to 0 and jiffies start
counting at -5 minutes, any clients connected in the first 5 minutes
after a reboot would have their renewal timer set to a very long
interval. If the connection was idle, this would result in the client
state timing out on the server and the next call to the server would
return NFS4ERR_BADSESSION.

Fix this by initializing the last renewal time to the current jiffies
instead of 0.

Signed-off-by: Joshua Watt <jpewhacker@gmail.com>
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>