net: page_pool: avoid false positive warning if NAPI was never added

We expect NAPI to be in disabled state when page pool is torn down.
But it is also legal if the NAPI is completely uninitialized.

Reviewed-by: Mina Almasry <almasrymina@google.com>
Link: https://patch.msgid.link/20250206225638.1387810-4-kuba@kernel.org


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