Some packetdrill tests are flaky in debug mode. As discussed, increase
tolerance.

We have been doing this for debug builds outside ksft too.

Previous setting was 10000. A manual 50 runs in virtme-ng showed two
failures that needed 12000. To be on the safe side, Increase to 14000.

Link: https://lore.kernel.org/netdev/Zuhhe4-MQHd3EkfN@mini-arch/
Fixes: 1e42f73f ("selftests/net: packetdrill: import tcp/zerocopy")
Reported-by: Stanislav Fomichev <sdf@fomichev.me>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Acked-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20240919124412.3014326-1-willemdebruijn.kernel@gmail.comSigned-off-by: Paolo Abeni <pabeni@redhat.com>