nfsd41: define nfsd4_set_statp as noop for !CONFIG_NFSD_V4

Fixes following modpost error:
ERROR: "nfsd4_set_statp" [fs/nfsd/nfsd.ko] undefined!

Signed-off-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>