s390/qeth: fix VLAN attribute in bridge_hostnotify udev event

Enabling sysfs attribute bridge_hostnotify triggers a series of udev events
for the MAC addresses of all currently connected peers. In case no VLAN is
set for a peer, the device reports the corresponding MAC addresses with
VLAN ID 4096. This currently results in attribute VLAN=4096 for all
non-VLAN interfaces in the initial series of events after host-notify is
enabled.

Instead, no VLAN attribute should be reported in the udev event for
non-VLAN interfaces.

Only the initial events face this issue. For dynamic changes that are
reported later, the device uses a validity flag.

This also changes the code so that it now sets the VLAN attribute for
MAC addresses with VID 0. On Linux, no qeth interface will ever be
registered with VID 0: Linux kernel registers VID 0 on all network
interfaces initially, but qeth will drop .ndo_vlan_rx_add_vid for VID 0.
Peers with other OSs could register MACs with VID 0.

Fixes: 9f48b9db ("qeth: bridgeport support - address notifications")
Signed-off-by: Alexandra Winter <wintera@linux.ibm.com>
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>