NFSv4.1: Don't call nfs4_schedule_state_recovery() unnecessarily

Currently, nfs4_handle_exception() will call it twice if called with an
error of -NFS4ERR_STALE_CLIENTID, -NFS4ERR_STALE_STATEID or
-NFS4ERR_EXPIRED.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Reviewed-by: Chuck Lever <chuck.lever@oracle.com>