NFSD: Add nfsd4_encode_fattr4_acl_trueform_scope

NFSD: Add nfsd4_encode_fattr4_acl_trueform_scope

The FATTR4_ACL_TRUEFORM_SCOPE attribute indicates the granularity at
which the ACL model can vary: per file object, per file system, or
uniformly across the entire server.

In Linux, the ACL model is determined by the SB_POSIXACL superblock
flag, which applies uniformly to all files within a file system.
Different exported file systems can have different ACL models, but
individual files cannot differ from their containing file system.
ACL_SCOPE_FILE_SYSTEM accurately reflects this behavior.

Signed-off-by: Rick Macklem <rmacklem@uoguelph.ca>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>