SUNRPC: Add a backpointer from the struct rpc_cred to the rpc_auth

Cleans up an issue whereby rpcsec_gss uses the rpc_clnt->cl_auth. If we want
to be able to add several rpc_auths to a single rpc_clnt, then this abuse
must go.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/include/linux/sunrpc/auth.h b/include/linux/sunrpc/auth.h
index 534cdc7..8ef27af 100644
--- a/include/linux/sunrpc/auth.h
+++ b/include/linux/sunrpc/auth.h
@@ -30,8 +30,11 @@
 /*
  * Client user credentials
  */
+struct rpc_auth;
+struct rpc_credops;
 struct rpc_cred {
 	struct hlist_node	cr_hash;	/* hash chain */
+	struct rpc_auth *	cr_auth;
 	struct rpc_credops *	cr_ops;
 	unsigned long		cr_expire;	/* when to gc */
 	atomic_t		cr_count;	/* ref count */
@@ -60,6 +63,7 @@
 	unsigned long		expire;		/* cache expiry interval */
 };
 
+struct rpc_authops;
 struct rpc_auth {
 	unsigned int		au_cslack;	/* call cred size estimate */
 				/* guess at number of u32's auth adds before