qeth: preallocated header account offset

When a preallocated header qdio buffer is filled we have to account
the offset for the data length.
Signed-off-by: Frank Blaschka <frank.blaschka@de.ibm.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/s390/net/qeth_core_main.c

@@ -3024,7 +3024,7 @@ static inline void __qeth_fill_buffer(struct sk_buff *skb,
 	struct qdio_buffer *buffer, int is_tso, int *next_element_to_fill,
 	int offset)
 {
-	int length = skb->len;
+	int length = skb->len - offset;
 	int length_here;
 	int element;
 	char *data;