SUNRPC: Cache cred of process creating the rpc_client

When converting kuids to AUTH_UNIX creds, etc we will want to use the
same user namespace as the process that created the rpc client.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

fs/nfsd/nfs4callback.c

@@ -868,6 +868,7 @@ static int setup_callback_client(struct nfs4_client *clp, struct nfs4_cb_conn *c
 		.program	= &cb_program,
 		.version	= 1,
 		.flags		= (RPC_CLNT_CREATE_NOPING | RPC_CLNT_CREATE_QUIET),
+		.cred		= current_cred(),
 	};
 	struct rpc_clnt *client;
 	const struct cred *cred;