NFS/NFSD/SUNRPC: replace generic creds with 'struct cred'.

SUNRPC has two sorts of credentials, both of which appear as
"struct rpc_cred".
There are "generic credentials" which are supplied by clients
such as NFS and passed in 'struct rpc_message' to indicate
which user should be used to authorize the request, and there
are low-level credentials such as AUTH_NULL, AUTH_UNIX, AUTH_GSS
which describe the credential to be sent over the wires.

This patch replaces all the generic credentials by 'struct cred'
pointers - the credential structure used throughout Linux.

For machine credentials, there is a special 'struct cred *' pointer
which is statically allocated and recognized where needed as
having a special meaning.  A look-up of a low-level cred will
map this to a machine credential.

Signed-off-by: NeilBrown <neilb@suse.com>
Acked-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

fs/nfs/pnfs_nfs.c

@@ -686,7 +686,7 @@ static int _nfs4_pnfs_v4_ds_connect(struct nfs_server *mds_srv,
 					  rpc_clnt_setup_test_and_add_xprt,
 					  &rpcdata);
 			if (xprtdata.cred)
-				put_rpccred(xprtdata.cred);
+				put_cred(xprtdata.cred);
 		} else {
 			clp = nfs4_set_ds_client(mds_srv,
 						(struct sockaddr *)&da->da_addr,