selftests: net: udpgso_bench_rx/tx: Stop when wrong CLI args are provided

selftests: net: udpgso_bench_rx/tx: Stop when wrong CLI args are provided

Leaving unrecognized arguments buried in the output, can easily hide a
CLI/script typo. Avoid this by exiting when wrong arguments are provided to
the udpgso_bench test programs.

Fixes: 3a687bef148d ("selftests: udp gso benchmark")
Signed-off-by: Andrei Gherzan <andrei.gherzan@canonical.com>
Cc: Willem de Bruijn <willemb@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/r/20230201001612.515730-2-andrei.gherzan@canonical.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>