s390/qeth: recognize non-IP multicast on L3 transmit

When
1. an skb has no neighbour, and
2. skb->protocol is not IP[V6],

we select the skb's cast type based on its destination MAC address.

The multicast check is currently restricted to Multicast IP-mapped MACs.
Extend it to also cover non-IP Multicast MACs.

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