NFSv4.1: Ensure that nfs41_walk_client_list() does start lease recovery

We do need to start the lease recovery thread prior to waiting for the
client initialisation to complete in NFSv4.1.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: Ben Greear <greearb@candelatech.com>
Cc: stable@vger.kernel.org [>=3.7]