page_pool: rename page_pool_return_page() to page_pool_return_netmem()

Now that page_pool_return_page() is for returning netmem, not struct
page, rename it to page_pool_return_netmem() to reflect what it does.

Signed-off-by: Byungchul Park <byungchul@sk.com>
Reviewed-by: Mina Almasry <almasrymina@google.com>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Link: https://patch.msgid.link/20250702053256.4594-2-byungchul@sk.com


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