devlink: Support DEVLINK_ESWITCH_MODE_SWITCHDEV_INACTIVE

devlink: Support DEVLINK_ESWITCH_MODE_SWITCHDEV_INACTIVE

Add support for the new inactive switchdev mode [1].

A user can start the eswitch in switchdev or switchdev_inactive mode.

Active: Traffic is enabled on this eswitch FDB.
Inactive: Traffic is ignored/dropped on this eswitch FDB.

An example use case:
$ devlink dev eswitch set pci/0000:08:00.1 mode switchdev_inactive
Setup FDB pipeline and netdev representors
...
Once ready to start receiving traffic
$ devlink dev eswitch set pci/0000:08:00.1 mode switchdev

[1] https://lore.kernel.org/all/20251107000831.157375-1-saeed@kernel.org/

Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: David Ahern <dsahern@kernel.org>