s390/qeth: use and remove some defines

1. a buffer has 16 is_header flags, because that's its # of elements
2. replace the last occurrence of QETH_HEADER_SIZE, and remove it

Signed-off-by: Julian Wiedmann <jwi@linux.vnet.ibm.com>
Acked-by: Ursula Braun <ubraun@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/s390/net/qeth_l2_main.c

@@ -280,7 +280,7 @@ static void qeth_l2_fill_header(struct qeth_card *card, struct qeth_hdr *hdr,
 	else
 		hdr->hdr.l2.flags[2] |= QETH_LAYER2_FLAG_UNICAST;
 
-	hdr->hdr.l2.pkt_length = skb->len-QETH_HEADER_SIZE;
+	hdr->hdr.l2.pkt_length = skb->len - sizeof(struct qeth_hdr);
 	/* VSWITCH relies on the VLAN
 	 * information to be present in
 	 * the QDIO header */