net/mlx5e: SHAMPO, Fix page_index calculation inconsistency

net/mlx5e: SHAMPO, Fix page_index calculation inconsistency

When calculating the index for the next frag page slot, the divisor is
incorrect: it should be the number of pages per queue not the number of
headers per queue. This is currently harmless because frag pages are not
used directly, but they are intermediated through the info array. But it
needs to be fixed as an upcoming patch will get rid of the info array.

This patch introduces a new pages per queue variable and plugs it in the
formula.

Now that this variable exists, additional code can be simplified in the
SHAMPO initialization code.

Signed-off-by: Dragos Tatulea <dtatulea@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/20241107194357.683732-10-tariqt@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>