net: veth: make PAGE_POOL_STATS optional

Since veth is very likely to be enabled and there are some drivers
(e.g. mlx5) where CONFIG_PAGE_POOL_STATS is optional, make
CONFIG_PAGE_POOL_STATS optional for veth too in order to keep it
optional instead of required.

Suggested-by: Jiri Benc <jbenc@redhat.com>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>