nfsd41: Refactor create_client()

Move common initialization of 'struct nfs4_client' inside create_client().

Signed-off-by: Ricardo Labiaga <Ricardo.Labiaga@netapp.com>

[nfsd41: Remember the auth flavor to use for callbacks]
Signed-off-by: Ricardo Labiaga <Ricardo.Labiaga@netapp.com>
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>