NFS: Correct size calculation for create reply length

CREATE requests return a post_op_fh3, rather than nfs_fh3. The
post_op_fh3 includes an extra word to indicate 'handle_follows'.

Without that additional word, create fails when full 64-byte
filehandles are in use.

Add NFS3_post_op_fh_sz, and correct the size calculation for
NFS3_createres_sz.

Signed-off-by: Frank Sorenson <sorenson@redhat.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>