s390/qeth: run non-offload L3 traffic over common xmit path

L3 OSAs can only offload IPv4 traffic, use the common L2 transmit path
for all other traffic.
In particular there's no support for TX VLAN offload, so any such packet
needs to be manually de-accelerated via ndo_features_check().

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