RPC: xdr_encode_pages either leaves the tail iovec pointing to

null or, if padding onthe page data is needed, sets it to point
to a little bit of static data. This is a problem if we're
expecting to later append some data in gss_wrap_req. Modify
xdr_encode_pages to make tail point to the end of the data in
head, as xdr_inline_pages and xdr_write_pages do.

net/sunrpc/xdr.c

@@ -107,16 +107,23 @@ void
 xdr_encode_pages(struct xdr_buf *xdr, struct page **pages, unsigned int base,
 		 unsigned int len)
 {
+	struct iovec *tail = xdr->tail;
+	u32 *p;
+
 	xdr->pages = pages;
 	xdr->page_base = base;
 	xdr->page_len = len;
 
+	p = (u32 *)xdr->head[0].iov_base + XDR_QUADLEN(xdr->head[0].iov_len);
+	tail->iov_base = p;
+	tail->iov_len = 0;
+
 	if (len & 3) {
-		struct iovec *iov = xdr->tail;
 		unsigned int pad = 4 - (len & 3);
 
-		iov->iov_base = (void *) "\0\0\0";
-		iov->iov_len  = pad;
+		*p = 0;
+		tail->iov_base = (char *)p + (len & 3);
+		tail->iov_len  = pad;
 		len += pad;
 	}
 	xdr->len += len;