SUNRPC: mark bulk read/write data in xdrbuf

Adds a flag word to the xdrbuf struct which indicates any bulk
disposition of the data. This enables RPC transport providers to
marshal it efficiently/appropriately, and may enable other
optimizations.

Signed-off-by: Tom Talpey <tmt@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

net/sunrpc/clnt.c

@@ -874,6 +874,7 @@ rpc_xdr_buf_init(struct xdr_buf *buf, void *start, size_t len)
 	buf->head[0].iov_len = len;
 	buf->tail[0].iov_len = 0;
 	buf->page_len = 0;
+	buf->flags = 0;
 	buf->len = 0;
 	buf->buflen = len;
 }