s390/qeth: reduce RX skb setup

Newly-allocated skbs default to PACKET_HOST, and eth_type_trans() is
smart enough to determine any other packet type from the frame's
destination address.
So except for the IQD sniffer case, there is no need to set up
skb->pkt_type manually.

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