rtnetlink: use for_each_netdev_dump() in rtnl_stats_dump()

Switch rtnl_stats_dump() to use for_each_netdev_dump()
instead of net->dev_index_head[] hash table.

This makes the code much easier to read, and fixes
scalability issues.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20240502113748.1622637-3-edumazet@google.com


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