NFS: Try AUTH_UNIX when PUTROOTFH gets NFS4ERR_WRONGSEC

Most NFSv4 servers implement AUTH_UNIX, and administrators will
prefer this over AUTH_NULL.  It is harmless for our client to try
this flavor in addition to the flavors mandated by RFC 3530/5661.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/nfs4proc.c

@@ -2531,6 +2531,7 @@ static int nfs4_find_root_sec(struct nfs_server *server, struct nfs_fh *fhandle,
 		RPC_AUTH_GSS_KRB5P,
 		RPC_AUTH_GSS_KRB5I,
 		RPC_AUTH_GSS_KRB5,
+		RPC_AUTH_UNIX,			/* courtesy */
 		RPC_AUTH_NULL,
 	};
 	int status = -EPERM;