s390/qeth: copy less data from bridge state events

Current code copies _all_ entries from the event into a worker, when we
later only need specific data from the first entry.

Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Reviewed-by: Alexandra Winter <wintera@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>