qeth: fix offset error in non prealloc header path

For the non preallocated qeth header code path we should not
change the header 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

@@ -3025,7 +3025,7 @@ 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 - offset;
+	int length = skb->len;
 	int length_here;
 	int element;
 	char *data;
@@ -3037,6 +3037,7 @@ static inline void __qeth_fill_buffer(struct sk_buff *skb,
 
 	if (offset >= 0) {
 		data = skb->data + offset;
+		length -= offset;
 		first_lap = 0;
 	}