eth: fbnic: link NAPIs to page pools

The lifetime of page pools is tied to NAPI instances,
and they are destroyed before NAPI is deleted.
It's safe to link them up.

Acked-by: Joe Damato <jdamato@fastly.com>
Link: https://patch.msgid.link/20250306145150.1757263-2-kuba@kernel.org


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