s390/qeth: remove VLAN tracking for L2 devices

For recovery purposes, qeth keeps track of all registered VIDs. Replace
this by using the infrastructure introduced in
commit 9daae9bd ("net: Call add/kill vid ndo on vlan filter feature toggling").

By managing NETIF_F_HW_VLAN_CTAG_FILTER as a hw_feature,
netdev_update_features() will select it from dev->wanted_features
and replay all of the netdevice's VIDs to its ndo_vlan_rx_add_vid()
callback.
z/VM NICs strictly require VLAN registration, so don't expose it as
hw_feature there but add a little hack in qeth_enable_hw_features()
to make things work regardless.

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