net: fix network drivers ndo_start_xmit() return values (part 5)

Fix up s390 drivers that return an errno value to qdisc_restart(), causing
qdisc_restart() to print a warning an requeue/retransmit the skb.

- claw: impossible condition, simply remove it

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>