Merge branch 'support-setting-lanes-via-ethtool'

Danielle Ratson says:

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Support setting lanes via ethtool

Some speeds can be achieved with different number of lanes. For example,
100Gbps can be achieved using two lanes of 50Gbps or four lanes of
25Gbps. This patchset adds a new selector that allows ethtool to
advertise link modes according to their number of lanes and also force a
specific number of lanes when autonegotiation is off.

Advertising all link modes with a speed of 100Gbps that use two lanes:

$ ethtool -s swp1 speed 100000 lanes 2 autoneg on

Forcing a speed of 100Gbps using four lanes:

$ ethtool -s swp1 speed 100000 lanes 4 autoneg off
====================

Link: https://lore.kernel.org/r/20210202180612.325099-1-danieller@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>