nfsd: Handle kuids and kgids in the nfs4acl to posix_acl conversion

In struct nfs4_ace remove the member who and replace it with an
anonymous union holding who_uid and who_gid.  Allowing typesafe
storage uids and gids.

Add a helper pace_gt for sorting posix_acl_entries.

In struct posix_user_ace_state to replace uid with a union
of kuid_t uid and kgid_t gid.

Remove all initializations of the deprecated posic_acl_entry
e_id field.  Which is not present when user namespaces are enabled.

Split find_uid into two functions find_uid and find_gid that work
in a typesafe manner.

In nfs4xdr update nfsd4_encode_fattr to deal with the changes
in struct nfs4_ace.

Rewrite nfsd4_encode_name to take a kuid_t and a kgid_t instead
of a generic id and flag if it is a group or a uid.  Replace
the group flag with a test for a valid gid.

Modify nfsd4_encode_user to take a kuid_t and call the modifed
nfsd4_encode_name.

Modify nfsd4_encode_group to take a kgid_t and call the modified
nfsd4_encode_name.

Modify nfsd4_encode_aclname to take an ace instead of taking the
fields of an ace broken out.  This allows it to detect if the ace is
for a user or a group and to pass the appropriate value while still
being typesafe.

Cc: "J. Bruce Fields" <bfields@fieldses.org>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
diff --git a/include/linux/nfs4.h b/include/linux/nfs4.h
index e111fa4..7b8fc73 100644
--- a/include/linux/nfs4.h
+++ b/include/linux/nfs4.h
@@ -13,6 +13,7 @@
 #define _LINUX_NFS4_H
 
 #include <linux/list.h>
+#include <linux/uidgid.h>
 #include <uapi/linux/nfs4.h>
 
 struct nfs4_ace {
@@ -20,7 +21,10 @@
 	uint32_t	flag;
 	uint32_t	access_mask;
 	int		whotype;
-	uid_t		who;
+	union {
+		kuid_t	who_uid;
+		kgid_t	who_gid;
+	};
 };
 
 struct nfs4_acl {