sunrpc: add a new "stringify_acceptor" rpc_credop

...and add an new rpc_auth function to call it when it exists. This
is only applicable for AUTH_GSS mechanisms, so we only specify this
for those sorts of credentials.

Signed-off-by: Jeff Layton <jlayton@poochiereds.net>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
diff --git a/net/sunrpc/auth.c b/net/sunrpc/auth.c
index f773667..1481eff 100644
--- a/net/sunrpc/auth.c
+++ b/net/sunrpc/auth.c
@@ -363,6 +363,15 @@
 }
 EXPORT_SYMBOL_GPL(rpcauth_cred_key_to_expire);
 
+char *
+rpcauth_stringify_acceptor(struct rpc_cred *cred)
+{
+	if (!cred->cr_ops->crstringify_acceptor)
+		return NULL;
+	return cred->cr_ops->crstringify_acceptor(cred);
+}
+EXPORT_SYMBOL_GPL(rpcauth_stringify_acceptor);
+
 /*
  * Destroy a list of credentials
  */