nfs_common: Update the translation between nfsv3 acls linux posix acls

- Use kuid_t and kgit in struct nfsacl_encode_desc.
- Convert from kuids and kgids when generating on the wire values.
- Convert on the wire values to kuids and kgids when read.
- Modify cmp_acl_entry to be type safe comparison on posix acls.
  Only acls with type ACL_USER and ACL_GROUP can appear more
  than once and as such need to compare more than their tag.
- The e_id field is being removed from posix acls so don't initialize it.

Cc: "J. Bruce Fields" <bfields@fieldses.org>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>