SUNRPC: Don't attempt to destroy expired RPCSEC_GSS credentials..

..and always destroy using a 'soft' RPC call. Destroying GSS credentials
isn't mandatory; the server can always cope with a few credentials not
getting destroyed in a timely fashion.

This actually fixes a hang situation. Basically, some servers will decide
that the client is crazy if it tries to destroy an RPC context for which
they have sent an RPCSEC_GSS_CREDPROBLEM, and so will refuse to talk to it
for a while.
The regression therefor probably was introduced by commit
0df7fb74.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

net/sunrpc/auth_gss/auth_gss.c

@@ -710,7 +710,7 @@ gss_destroying_context(struct rpc_cred *cred)
 	struct rpc_task *task;
 
 	if (gss_cred->gc_ctx == NULL ||
-			gss_cred->gc_ctx->gc_proc == RPC_GSS_PROC_DESTROY)
+	    test_and_clear_bit(RPCAUTH_CRED_UPTODATE, &cred->cr_flags) == 0)
 		return 0;
 
 	gss_cred->gc_ctx->gc_proc = RPC_GSS_PROC_DESTROY;
@@ -720,7 +720,7 @@ gss_destroying_context(struct rpc_cred *cred)
 	 * by the RPC call or by the put_rpccred() below */
 	get_rpccred(cred);
 
-	task = rpc_call_null(gss_auth->client, cred, RPC_TASK_ASYNC);
+	task = rpc_call_null(gss_auth->client, cred, RPC_TASK_ASYNC|RPC_TASK_SOFT);
 	if (!IS_ERR(task))
 		rpc_put_task(task);