mlxsw: spectrum_switchdev: Use tracker helpers to hold & put netdevices

Using the tracking helpers makes it easier to debug netdevice refcount
imbalances when CONFIG_NET_DEV_REFCNT_TRACKER is enabled.

Convert dev_hold() / dev_put() to netdev_hold() / netdev_put() in the
switchdev module.

Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/774c3d7b5b0231f1435df2ec9dd660192e382756.1690471774.git.petrm@nvidia.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>