CIFS: Send RFC1001 length in a separate iov

In order to simplify further encryption support we need to separate
RFC1001 length and SMB2 header when sending a request. Put the length
field in iov[0] and the rest of the packet into following iovs.

Signed-off-by: Pavel Shilovsky <pshilov@microsoft.com>
diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index 6d5fc87..eb0ffac 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -1119,7 +1119,7 @@ struct cifs_readdata {
 	int (*read_into_pages)(struct TCP_Server_Info *server,
 				struct cifs_readdata *rdata,
 				unsigned int len);
-	struct kvec			iov;
+	struct kvec			iov[2];
 	unsigned int			pagesz;
 	unsigned int			tailsz;
 	unsigned int			credits;