eth: mlx4: use the page pool for Rx buffers

Simple conversion to page pool. Preserve the current fragmentation
logic / page splitting. Each page starts with a single frag reference,
and then we bump that when attaching to skbs. This can likely be
optimized further.

Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/20250213010635.1354034-5-kuba@kernel.org


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