selftests: forwarding: ethtool: Skip when using veth pairs

Auto-negotiation cannot be tested with veth pairs, resulting in
failures:

# ./ethtool.sh
TEST: force of same speed autoneg off [FAIL]
error in configuration. swp1 speed Not autoneg off
[...]

Fix by skipping the test when used with veth pairs.

Fixes: 64916b57c0b1 ("selftests: forwarding: Add speed and auto-negotiation test")
Reported-by: Mirsad Todorovac <mirsad.todorovac@alu.unizg.hr>
Closes: https://lore.kernel.org/netdev/adc5e40d-d040-a65e-eb26-edf47dac5b02@alu.unizg.hr/
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Tested-by: Mirsad Todorovac <mirsad.todorovac@alu.unizg.hr>
Reviewed-by: Hangbin Liu <liuhangbin@gmail.com>
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Link: https://lore.kernel.org/r/20230808141503.4060661-8-idosch@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

selftests: ethtool: Fix test when only two speeds are supported

The test case check_highest_speed_is_chosen() configures $h1 to
advertise a subset of its supported speeds and checks that $h2 chooses
the highest speed from the subset.

To find the common advertised speeds between $h1 and $h2,
common_speeds_get() is called.

Currently, the first speed returned from common_speeds_get() is removed
claiming "h1 does not advertise this speed". The claim is wrong because
the function is called after $h1 already advertised a subset of speeds.

In case $h1 supports only two speeds, it will advertise a single speed
which will be later removed because of previously mentioned bug. This
results in the test needlessly failing. When more than two speeds are
supported this is not an issue because the first advertised speed
is the lowest one.

Fix this by not removing any speed from the list of commonly advertised
speeds.

Fixes: 64916b57c0b1 ("selftests: forwarding: Add speed and auto-negotiation test")
Reported-by: Danielle Ratson <danieller@mellanox.com>
Signed-off-by: Amit Cohen <amitc@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

selftests: forwarding: ethtool: Move different_speeds_get() to ethtool_lib

Currently different_speeds_get() is used only by ethtool.sh tests.
The function can be useful for another tests that check ethtool
configurations.

Move the function to ethtool_lib in order to allow other tests to use
it.

Signed-off-by: Amit Cohen <amitc@mellanox.com>
Reviewed-by: Petr Machata <petrm@mellanox.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

selftests: forwarding: Add speed and auto-negotiation test

Check configurations and packets transference with different variations
of autoneg and speed.

Test plan:
1. Test force of same speed with autoneg off
2. Test force of different speeds with autoneg off (should fail)
3. One side is autoneg on and other side sets force of common speeds
4. One side is autoneg on and other side only advertises a subset of the
common speeds (one speed of the subset)
5. One side is autoneg on and other side only advertises a subset of the
common speeds. Check that highest speed is negotiated
6. Test autoneg on, but each side advertises different speeds (should
fail)

Signed-off-by: Amit Cohen <amitc@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>