qeth: do not turn on SG per default

According to recent performance measurements, turning on net_device
feature NETIF_F_SG only behaves well, but turning on feature
NETIF_F_GSO shows bad results. Since the kernel activates NETIF_F_GSO
automatically as soon as the driver configures feature NETIF_F_SG, qeth
should not activate feature NETIF_F_SG per default, until the qeth
problems with NETIF_F_GSO are solved.

Signed-off-by: Ursula Braun <ubraun@linux.vnet.ibm.com>
Reviewed-by: Thomas Richter <tmricht@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>