qeth: Clear mac_bits field when switching between Layer 2 and Layer 3

This patch fixes a problem that occurs when switching from layer 3 to layer 2
mode. Resetting this mac_bits makes sure that we retrieve our mac address from
the card, otherwise the interface simply would'nt work.
Signed-off-by: NCarsten Otte <cotte@de.ibm.com>
Signed-off-by: NFrank Blaschka <frank.blaschka@de.ibm.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/s390/net/qeth_core_sys.c

@@ -433,6 +433,7 @@ static ssize_t qeth_dev_layer2_store(struct device *dev,
 	if (card->options.layer2 == newdis)
 		goto out;
 	else {
+		card->info.mac_bits  = 0;
 		if (card->discipline.ccwgdriver) {
 			card->discipline.ccwgdriver->remove(card->gdev);
 			qeth_core_free_discipline(card);