selftests/net: pass ipv6_args to udpgso_bench's IPv6 TCP test

udpgso_bench.sh has been running its IPv6 TCP test with IPv4 arguments
since its initial conmit. Looks like a typo.

Fixes: 3a687bef ("selftests: udp gso benchmark")
Cc: willemb@google.com
Signed-off-by: Dimitris Michailidis <dmichail@fungible.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/r/20220623000234.61774-1-dmichail@fungible.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>