selftests: forwarding: Add a test for NH group stats

Add to lib.sh support for fetching NH stats, and a new library,
router_mpath_nh_lib.sh, with the common code for testing NH stats.
Use the latter from router_mpath_nh.sh and router_mpath_nh_res.sh.

The test works by sending traffic through a NH group, and checking that the
reported values correspond to what the link that ultimately receives the
traffic reports having seen.

Signed-off-by: Petr Machata <petrm@nvidia.com>
Link: https://lore.kernel.org/r/2a424c54062a5f1efd13b9ec5b2b0e29c6af2574.1709901020.git.petrm@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

selftests: forwarding: Parametrize mausezahn delay

The various multipath tests use mausezahn to generate different flows
and check how they are distributed between the available nexthops. The
tool is currently invoked with an hard coded transmission delay of 1 ms.
This is unnecessary when the tests are run with veth pairs and
needlessly prolongs the tests.

Parametrize this delay and default it to 0 us. It can be overridden
using the forwarding.config file. On my system, this reduces the run
time of router_multipath.sh by 93%.

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Link: https://lore.kernel.org/r/20240304095612.462900-3-idosch@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

selftests/net: Use kselftest skip code for skipped tests

There are several test cases in the net directory are still using
exit 0 or exit 1 when they need to be skipped. Use kselftest
framework skip code instead so it can help us to distinguish the
return status.

Criterion to filter out what should be fixed in net directory:
grep -r "exit [01]" -B1 | grep -i skip

This change might cause some false-positives if people are running
these test scripts directly and only checking their return codes,
which will change from 0 to 4. However I think the impact should be
small as most of our scripts here are already using this skip code.
And there will be no such issue if running them with the kselftest
framework.

Signed-off-by: Po-Hsu Lin <po-hsu.lin@canonical.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Tested-by: Ido Schimmel <idosch@nvidia.com>
Link: https://lore.kernel.org/r/20210823085854.40216-1-po-hsu.lin@canonical.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

selftests: forwarding: Add resilient hashing test

Verify that IPv4 and IPv6 multipath forwarding works correctly with
resilient nexthop groups and with different weights.

Test that when the idle timer is not zero, the resilient groups are not
rebalanced - because the nexthop buckets are considered active - and the
initial weights (1:1) are used.

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>