selftests: net: let big_tcp test cope with slow env

In very slow environments, most big TCP cases including
segmentation and reassembly of big TCP packets have a good
chance to fail: by default the TCP client uses write size
well below 64K. If the host is low enough autocorking is
unable to build real big TCP packets.

Address the issue using much larger write operations.

Note that is hard to observe the issue without an extremely
slow and/or overloaded environment; reduce the TCP transfer
time to allow for much easier/faster reproducibility.

Fixes: 6bb382bcf742 ("selftests: add a selftest for big tcp")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Acked-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

selftests: add a selftest for big tcp

This test runs on the client-router-server topo, and monitors the traffic
on the RX devices of router and server while sending BIG TCP packets with
netperf from client to server. Meanwhile, it changes 'tso' on the TX devs
and 'gro' on the RX devs. Then it checks if any BIG TCP packets appears
on the RX devs with 'ip/ip6tables -m length ! --length 0:65535' for each
case.

Note that we also add tc action ct in link1 ingress to cover the ipv6
jumbo packets process in nf_ct_skb_network_trim() of nf_conntrack_ovs.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Reviewed-by: Aaron Conole <aconole@redhat.com>
Reviewed-by: Nikolay Aleksandrov <razor@blackwall.org>
Signed-off-by: Florian Westphal <fw@strlen.de>