selftests: in udpgso_bench do not test udp zerocopy

The udpgso benchmark compares various configurations of UDP and TCP.
Including one that is not upstream, udp zerocopy. This is a leftover
from the earlier RFC patchset.

The test is part of kselftests and run in continuous spinners. Remove
the failing case to make the test start passing.

Fixes: 3a687bef

 ("selftests: udp gso benchmark")
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>