s390/qeth: remove RX VLAN filter stubs in L3 driver

The callbacks have been slimmed down to a level where they no longer do
any actual work. So stop pretending that we support the
NETIF_F_HW_VLAN_CTAG_FILTER feature.

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