net: core: add devm_netdev_alloc_pcpu_stats

We have netdev_alloc_pcpu_stats(), and we have devm_alloc_percpu().
Add a managed version of netdev_alloc_pcpu_stats, e.g. for allocating
the per-cpu stats in the probe() callback of a driver. It needs to be
a macro for dealing properly with the type argument.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>