net: page_pool: simplify page recycling condition tests

pool_page_reusable() is a leftover from pre-NUMA-aware times. For now,
this function is just a redundant wrapper over page_is_pfmemalloc(),
so inline it into its sole call site.

Signed-off-by: Alexander Lobakin <alobakin@pm.me>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>