vfs_nfs4acl_xattr: support for NFS 4.0 and 4.1 ACLs from NFS4 mount

vfs_nfs4acl_xattr: support for NFS 4.0 and 4.1 ACLs from NFS4 mount

This adds a new main switch "nfs" to "nfs4acl_xattr:encoding" which
enables to use NFS4 ACLs from an NFS4 mount on a Linux box. Tested with
a FreeBSD NFS4 server.

Supports both NFS 4.0 and 4.1 ACLs.

By default NFS4 servers send user and group identifiers in ACLs as
strings in the format "[USER|GROUP]@DNSDOMAIN". Some NFS4 servers
support sending identifiers as numeric strings. This module does support
this as well, the config knob "nfs4acl_xattr:nfs4_id_numeric = yes|no"
controls behaviour.

When "nfs4acl_xattr:encoding" is set to "nfs", the new option
"nfs4acl_xattr:validate_mode", which defauts to "yes" is set to "no" to
avoid checking and munging the mode on files.

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>