NFS: Fix initialisation of nfs_client cl_flags field

For some long forgotten reason, the nfs_client cl_flags field is
initialised in nfs_get_client() instead of being initialised at
allocation time. This quirk was harmless until we moved the call to
nfs_create_rpc_client().

Fixes: dd99e9f9

 ("NFSv4: Initialise connection to the server in nfs4_alloc_client()")
Cc: stable@vger.kernel.org # 4.8.x
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>