SUNRPC: Retry bad rpcbind replies

When a server returns a bad rpcbind reply, make rpcbind client recovery logic
retry with an older protocol version.  Older versions are more likely to work
correctly.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/net/sunrpc/rpcb_clnt.c b/net/sunrpc/rpcb_clnt.c
index 34738c5..a0c9f69 100644
--- a/net/sunrpc/rpcb_clnt.c
+++ b/net/sunrpc/rpcb_clnt.c
@@ -446,6 +446,10 @@
 	struct rpc_xprt *xprt = map->r_xprt;
 	int status = child->tk_status;
 
+	/* Garbage reply: retry with a lesser rpcbind version */
+	if (status == -EIO)
+		status = -EPROTONOSUPPORT;
+
 	/* rpcbind server doesn't support this rpcbind protocol version */
 	if (status == -EPROTONOSUPPORT)
 		xprt->bind_index++;