sunrpc: gss_pipe_downcall(), don't assume all errors are transient

Instead of mapping all errors except EACCES to EAGAIN, map all errors
except EAGAIN to EACCES.

An example is user-land negotiating a Kerberos context with an encryption
type that is not supported by the kernel code.  (This can happen due to
mis-configuration or a bug in the Kerberos code that does not honor our
request to limit the encryption types negotiated.)  This failure is not
transient, and returning EAGAIN causes mount to continuously retry rather
than giving up.
Signed-off-by: NKevin Coffman <kwc@citi.umich.edu>
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

net/sunrpc/auth_gss/auth_gss.c

@@ -540,7 +540,7 @@ gss_pipe_downcall(struct file *filp, const char __user *src, size_t mlen)
 	p = gss_fill_context(p, end, ctx, gss_msg->auth->mech);
 	if (IS_ERR(p)) {
 		err = PTR_ERR(p);
-		gss_msg->msg.errno = (err == -EACCES) ? -EACCES : -EAGAIN;
+		gss_msg->msg.errno = (err == -EAGAIN) ? -EAGAIN : -EACCES;
 		goto err_release_msg;
 	}
 	gss_msg->ctx = gss_get_ctx(ctx);