netdevsim: access ->pp through netmem_desc instead of page

To eliminate the use of struct page in page pool, the page pool users
should use netmem descriptor and APIs instead.

Make netdevsim access ->pp through netmem_desc instead of page.

Signed-off-by: Byungchul Park <byungchul@sk.com>
Link: https://patch.msgid.link/20250721021835.63939-5-byungchul@sk.com


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