s390/qeth: don't raise NETDEV_REBOOT event from L3 offline path

This is a leftover from back when a recovery action didn't go through
dev_close(), and was meant to shoot down all remaining af_iucv sockets
on the interface.

Now that the offline path always calls dev_close(), the
NETDEV_GOING_DOWN event from __dev_close_many() is sufficient and this
hack can be removed.

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